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

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

third_party/git/Documentation/RelNotes/1.5.1.1.txt

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+GIT v1.5.1.1 Release Notes
+==========================
+
+Fixes since v1.5.1
+------------------
+
+* Documentation updates
+
+  - The --left-right option of rev-list and friends is documented.
+
+  - The documentation for cvsimport has been majorly improved.
+
+  - "git-show-ref --exclude-existing" was documented.
+
+* Bugfixes
+
+  - The implementation of -p option in "git cvsexportcommit" had
+    the meaning of -C (context reduction) option wrong, and
+    loosened the context requirements when it was told to be
+    strict.
+
+  - "git cvsserver" did not behave like the real cvsserver when
+    client side removed a file from the working tree without
+    doing anything else on the path.  In such a case, it should
+    restore it from the checked out revision.
+
+  - "git fsck" issued an alarming error message on detached
+    HEAD.  It is not an error since at least 1.5.0.
+
+  - "git send-email" produced of References header of unbounded length;
+    fixed this with line-folding.
+
+  - "git archive" to download from remote site should not
+    require you to be in a git repository, but it incorrectly
+    did.
+
+  - "git apply" ignored -p<n> for "diff --git" formatted
+    patches.
+
+  - "git rerere" recorded a conflict that had one side empty
+    (the other side adds) incorrectly; this made merging in the
+    other direction fail to use previously recorded resolution.
+
+  - t4200 test was broken where "wc -l" pads its output with
+    spaces.
+
+  - "git branch -m old new" to rename branch did not work
+    without a configuration file in ".git/config".
+
+  - The sample hook for notification e-mail was misnamed.
+
+  - gitweb did not show type-changing patch correctly in the
+    blobdiff view.
+
+  - git-svn did not error out with incorrect command line options.
+
+  - git-svn fell into an infinite loop when insanely long commit
+    message was found.
+
+  - git-svn dcommit and rebase was confused by patches that were
+    merged from another branch that is managed by git-svn.
+
+  - git-svn used to get confused when globbing remote branch/tag
+    spec (e.g. "branches = proj/branches/*:refs/remotes/origin/*")
+    is used and there was a plain file that matched the glob.