v1.8.5-rc0: An early preview of the upcoming release

There are many little changes everywhere.  All of the fixes that have already went into 1.8.4.2 maintenance release are also in this preview.

Foreign interfaces, subsystems and ports.

• "git-svn" used with SVN 1.8.0 when talking over https:// connection dumped core due to a bug in the serf library that SVN uses.  Work it around on our side, even though the SVN side is being fixed.
• On MacOS X, we detected if the filesystem needs the "pre-composed unicode strings" workaround, but did not automatically enable it.  Now we do.
• remote-hg remote helper misbehaved when interacting with a local Hg repository relative to the home directory, e.g. "clone hg::~/there".
• imap-send ported to OS X uses Apple's security framework instead of OpenSSL one.
• Subversion 1.8.0 that was recently released breaks older subversion clients coming over http/https in various ways.
• "git fast-import" treats an empty path given to "ls" as the root of the tree.

UI, Workflows & Features

• "git grep" and "git show" pays attention to "--textconv" option when these commands are told to operate on blob objects (e.g. "git grep -e pattern HEAD:Makefile").
• "git replace" helper no longer allows an object to be replaced with another object of a different type to avoid confusion (you can still manually craft such replacement using "git update-ref", as an escape hatch).
• "git status" no longer prints dirty status information for submodules for which submodule.$name.ignore is set to "all".
• "git rebase -i" honours core.abbrev when preparing the insn sheet for editing.
• "git status" during a cherry-pick shows what original commit is being picked.
• Instead of typing four capital letters "HEAD", you can say "@" now, e.g. "git log @".
• "git check-ignore" follows the same rule as "git add" and "git status" in that the ignore/exclude mechanism does not take effect on paths that are already tracked.  With "--no-index" option, it can be used to diagnose which paths that should have been ignored have been mistakenly added to the index.
• Some irrelevant "advice" messages that are shared with "git status" output have been removed from the commit log template.
• "update-refs" learnt a "--stdin" option to read multiple update requests and perform them in an all-or-none fashion.
• Just like "make -C <directory>", "git -C <directory> ..." tells Git to go there before doing anything else.
• Just like "git checkout -" knows to check out and "git merge -" knows to merge the branch you were previously on, "git cherry-pick" now understands "git cherry-pick -" to pick from the previous branch.
• "git status" now omits the prefix to make its output a comment in a commit log editor, which is not necessary for human consumption.  Scripts that parse the output of "git status" are advised to use "git status --porcelain" instead, as its format is stable and easier to parse.
• Make "foo^{tag}" to peel a tag to itself, i.e. no-op., and fail if "foo" is not a tag.  "git rev-parse --verify v1.0^{tag}" would be a more convenient way to say "test $(git cat-file -t v1.0) = tag".
• "git branch -v -v" (and "git status") did not distinguish among a branch that does not build on any other branch, a branch that is in sync with the branch it builds on, and a branch that is configured to build on some other branch that no longer exists.
• A packfile that stores the same object more than once is broken and will be rejected by "git index-pack" that is run when receiving data over the wire.
• Earlier we started rejecting an attempt to add 0{40} object name to the index and to tree objects, but it sometimes is necessary to allow so to be able to use tools like filter-branch to correct such broken tree objects.  "filter-branch" can again be used to to do so.
• "git config" did not provide a way to set or access numbers larger than a native "int" on the platform; it now provides 64-bit signed integers on all platforms.
• "git pull --rebase" always chose to do the bog-standard flattening rebase.  You can tell it to run "rebase --preserve-merges" by setting "pull.rebase" configuration to "preserve".
• "git push --no-thin" actually disables the "thin pack transfer" optimization.
• Magic pathspecs like ":(icase)makefile" that matches both Makefile and makefile can be used in more places.
• The "http.*" variables can now be specified per URL that the configuration applies.  For example,
  
     [http]
         sslVerify = true
     [http "https://weak.example.com/"]
         sslVerify = false
  would flip http.sslVerify off only when talking to that specified site.
• "git mv A B" when moving a submodule A has been taught to relocate its working tree and to adjust the paths in the .gitmodules file.
• "git blame" can now take more than one -L option to discover the origin of multiple blocks of the lines.
• The http transport clients can optionally ask to save cookies with http.savecookies configuration variable.
• "git push" learned a more fine grained control over a blunt "--force" when requesting a non-fast-forward update with the "--force-with-lease=<refname>:<expected object name>" option.
• "git diff --diff-filter=<classes of changes>" can now take lowercase letters (e.g. "--diff-filter=d") to mean "show everything but these classes".  "git diff-files -q" is now a deprecated synonym for "git diff-files --diff-filter=d".
• "git fetch" (hence "git pull" as well) learned to check "fetch.prune" and "remote.*.prune" configuration variables and to behave as if the "--prune" command line option was given.
• "git check-ignore -z" applied the NUL termination to both its input (with --stdin) and its output, but "git check-attr -z" ignored the option on the output side. Make both honor -z on the input and output side the same way.
• "git whatchanged" may still be used by old timers, but mention of it in documents meant for new users will only waste readers' time wonderig what the difference is between it and "git log".  Make it less prominent in the general part of the documentation and explain that it is merely a "git log" with different default behaviour in its own document.

Performance, Internal Implementation, etc.

• The HTTP transport will try to use TCP keepalive when able.
• "git repack" is now written in C.
• Build procedure for MSVC has been updated.
• If a build-time fallback is set to "cat" instead of "less", we should apply the same "no subprocess or pipe" optimization as we apply to user-supplied GIT_PAGER=cat.
• Many commands use --dashed-option as a operation mode selector (e.g. "git tag --delete") that the user can use at most one (e.g. "git tag --delete --verify" is a nonsense) and you cannot negate (e.g. "git tag --no-delete" is a nonsense).  parse-options API learned a new OPT_CMDMODE macro to make it easier to implement such a set of options.
• OPT_BOOLEAN() in parse-options API was misdesigned to be "counting up" but many subcommands expect it to behave as "on/off". Update them to use OPT_BOOL() which is a proper boolean.
• "git gc" exits early without doing a double-work when it detects that another instance of itself is already running.
• Under memory pressure and/or file descriptor pressure, we used to close pack windows that are not used and also closed filehandle to an open but unused packfiles. These are now controlled separately to better cope with the load.