Update to 2.5.1:

Git v2.5.1 Release Notes
========================

Fixes since v2.5
----------------

* Running an aliased command from a subdirectory when the .git thing
  in the working tree is a gitfile pointing elsewhere did not work.

* Often a fast-import stream builds a new commit on top of the
  previous commit it built, and it often unconditionally emits a
  "from" command to specify the first parent, which can be omitted in
  such a case.  This caused fast-import to forget the tree of the
  previous commit and then re-read it from scratch, which was
  inefficient.  Optimize for this common case.

* The "rev-parse --parseopt" mode parsed the option specification
  and the argument hint in a strange way to allow '=' and other
  special characters in the option name while forbidding them from
  the argument hint.  This made it impossible to define an option
  like "--pair <key>=<value>" with "pair=key=value" specification,
  which instead would have defined a "--pair=key <value>" option.

* A "rebase" replays changes of the local branch on top of something
  else, as such they are placed in stage #3 and referred to as
  "theirs", while the changes in the new base, typically a foreign
  work, are placed in stage #2 and referred to as "ours".  Clarify
  the "checkout --ours/--theirs".

* An experimental "untracked cache" feature used uname(2) in a
  slightly unportable way.

* "sparse checkout" misbehaved for a path that is excluded from the
  checkout when switching between branches that differ at the path.

* The low-level "git send-pack" did not honor 'user.signingkey'
  configuration variable when sending a signed-push.

* An attempt to delete a ref by pushing into a repository whose HEAD
  symbolic reference points at an unborn branch that cannot be
  created due to ref D/F conflict (e.g. refs/heads/a/b exists, HEAD
  points at refs/heads/a) failed.

* "git subtree" (in contrib/) depended on "git log" output to be
  stable, which was a no-no.  Apply a workaround to force a
  particular date format.

* "git clone $URL" in recent releases of Git contains a regression in
  the code that invents a new repository name incorrectly based on
  the $URL.  This has been corrected.
  (merge db2e220 jk/guess-repo-name-regression-fix later to maint).

* Running tests with the "-x" option to make them verbose had some
  unpleasant interactions with other features of the test suite.
  (merge 9b5fe78 jk/test-with-x later to maint).

* "git pull" in recent releases of Git has a regression in the code
  that allows custom path to the --upload-pack=<program>.  This has
  been corrected.

* pipe() emulation used in Git for Windows looked at a wrong variable
  when checking for an error from an _open_osfhandle() call.

Also contains typofixes, documentation updates and trivial code
clean-ups.

(wiz)