Sync with 2.14.6

* maint-2.14: (28 commits)
  Git 2.14.6
  mingw: handle `subst`-ed "DOS drives"
  mingw: refuse to access paths with trailing spaces or periods
  mingw: refuse to access paths with illegal characters
  unpack-trees: let merged_entry() pass through do_add_entry()'s errors
  quote-stress-test: offer to test quoting arguments for MSYS2 sh
  t6130/t9350: prepare for stringent Win32 path validation
  quote-stress-test: allow skipping some trials
  quote-stress-test: accept arguments to test via the command-line
  tests: add a helper to stress test argument quoting
  mingw: fix quoting of arguments
  Disallow dubiously-nested submodule git directories
  protect_ntfs: turn on NTFS protection by default
  path: also guard `.gitmodules` against NTFS Alternate Data Streams
  is_ntfs_dotgit(): speed it up
  mingw: disallow backslash characters in tree objects' file names
  path: safeguard `.git` against NTFS Alternate Streams Accesses
  clone --recurse-submodules: prevent name squatting on Windows
  is_ntfs_dotgit(): only verify the leading segment
  test-path-utils: offer to run a protectNTFS/protectHFS benchmark
  ...

submodule.h

@@ -111,6 +111,11 @@ extern void connect_work_tree_and_git_dir(const char *work_tree, const char *git
  */
 int submodule_to_gitdir(struct strbuf *buf, const char *submodule);
 
+/*
+ * Make sure that no submodule's git dir is nested in a sibling submodule's.
+ */
+int validate_submodule_git_dir(char *git_dir, const char *submodule_name);
+
 #define SUBMODULE_MOVE_HEAD_DRY_RUN (1<<0)
 #define SUBMODULE_MOVE_HEAD_FORCE   (1<<1)
 extern int submodule_move_head(const char *path,