Merge branch 'bc/master-diff-hunk-header-fix'

* bc/master-diff-hunk-header-fix:
  Clarify commit error message for unmerged files
  Use strchrnul() instead of strchr() plus manual workaround
  Use remove_path from dir.c instead of own implementation
  Add remove_path: a function to remove as much as possible of a path
  git-submodule: Fix "Unable to checkout" for the initial 'update'
  Clarify how the user can satisfy stash's 'dirty state' check.
  t4018-diff-funcname: test syntax of builtin xfuncname patterns
  t4018-diff-funcname: test syntax of builtin xfuncname patterns
  make "git remote" report multiple URLs
  diff hunk pattern: fix misconverted "\{" tex macro introducers
  diff: fix "multiple regexp" semantics to find hunk header comment
  diff: use extended regexp to find hunk headers
  diff: use extended regexp to find hunk headers
  diff.*.xfuncname which uses "extended" regex's for hunk header selection
  diff.c: associate a flag with each pattern and use it for compiling regex
  diff.c: return pattern entry pointer rather than just the hunk header pattern

Conflicts:
	builtin-merge-recursive.c
	t/t7201-co.sh
	xdiff-interface.h

builtin-commit.c

@@ -639,7 +639,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix)
 		active_cache_tree = cache_tree();
 	if (cache_tree_update(active_cache_tree,
 			      active_cache, active_nr, 0, 0) < 0) {
-		error("Error building trees");
+		error("Error building trees; the index is unmerged?");
 		return 0;
 	}