Sync with 2.5.3

* maint:
  Git 2.5.3

Documentation/RelNotes/2.5.3.txt

@@ -0,0 +1,17 @@
+Git v2.5.3 Release Notes
+========================
+
+Fixes since v2.5.2
+------------------
+
+ * The experimental untracked-cache feature were buggy when paths with
+   a few levels of subdirectories are involved.
+
+ * Recent versions of scripted "git am" has a performance regression
+   in "git am --skip" codepath, which no longer exists in the
+   built-in version on the 'master' front.  Fix the regression in
+   the last scripted version that appear in 2.5.x maintenance track
+   and older.
+
+Also contains typofixes, documentation updates and trivial code
+clean-ups.