Sync with Git 2.13.7

* maint-2.13:
  Git 2.13.7
  verify_path: disallow symlinks in .gitmodules
  update-index: stat updated files earlier
  verify_dotfile: mention case-insensitivity in comment
  verify_path: drop clever fallthrough
  skip_prefix: add case-insensitive variant
  is_{hfs,ntfs}_dotgitmodules: add tests
  is_ntfs_dotgit: match other .git files
  is_hfs_dotgit: match other .git files
  is_ntfs_dotgit: use a size_t for traversing string
  submodule-config: verify submodule names as paths

Documentation/RelNotes/2.13.7.txt

@@ -0,0 +1,20 @@
+Git v2.13.7 Release Notes
+=========================
+
+Fixes since v2.13.6
+-------------------
+
+ * Submodule "names" come from the untrusted .gitmodules file, but we
+   blindly append them to $GIT_DIR/modules to create our on-disk repo
+   paths. This means you can do bad things by putting "../" into the
+   name. We now enforce some rules for submodule names which will cause
+   Git to ignore these malicious names (CVE-2018-11235).
+
+   Credit for finding this vulnerability and the proof of concept from
+   which the test script was adapted goes to Etienne Stalmans.
+
+ * It was possible to trick the code that sanity-checks paths on NTFS
+   into reading random piece of memory (CVE-2018-11233).
+
+Credit for fixing for these bugs goes to Jeff King, Johannes
+Schindelin and others.