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

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

third_party/git/Documentation/RelNotes/1.5.2.5.txt

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+GIT v1.5.2.5 Release Notes
+==========================
+
+Fixes since v1.5.2.4
+--------------------
+
+ * Bugfixes
+
+   - "git add -u" had a serious data corruption problem in one
+     special case (when the changes to a subdirectory's files
+     consist only deletion of files).
+
+   - "git add -u <path>" did not work from a subdirectory.
+
+   - "git apply" left an empty directory after all its files are
+     renamed away.
+
+   - "git $anycmd foo/bar", when there is a file 'foo' in the
+     working tree, complained that "git $anycmd foo/bar --" form
+     should be used to disambiguate between revs and files,
+     which was completely bogus.
+
+   - "git checkout-index" and other commands that checks out
+     files to the work tree tried unlink(2) on directories,
+     which is a sane thing to do on sane systems, but not on
+     Solaris when you are root.
+
+ * Documentation Fixes and Updates
+
+   - A handful documentation fixes.