merge(third_party/git): Merge squashed git subtree at v2.23.0

Merge commit '1b593e1ea4' as 'third_party/git'

third_party/git/Documentation/RelNotes/1.5.4.3.txt

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+GIT v1.5.4.3 Release Notes
+==========================
+
+Fixes since v1.5.4.2
+--------------------
+
+ * RPM spec used to pull in everything with 'git'.  This has been
+   changed so that 'git' package contains just the core parts,
+   and we now supply 'git-all' metapackage to slurp in everything.
+   This should match end user's expectation better.
+
+ * When some refs failed to update, git-push reported "failure"
+   which was unclear if some other refs were updated or all of
+   them failed atomically (the answer is the former).  Reworded
+   the message to clarify this.
+
+ * "git clone" from a repository whose HEAD was misconfigured
+   did not set up the remote properly.  Now it tries to do
+   better.
+
+ * Updated git-push documentation to clarify what "matching"
+   means, in order to reduce user confusion.
+
+ * Updated git-add documentation to clarify "add -u" operates in
+   the current subdirectory you are in, just like other commands.
+
+ * git-gui updates to work on OSX and Windows better.