commit: pay attention to submodule.$name.ignore in .gitmodules

"git status" does not list a submodule with uncommitted working tree
files as modified when "submodule.$name.ignore" is set to "dirty" in
in-tree ".gitmodules" file.  Both status and commit honor the setting
in $GIT_DIR/config, but "commit" does not pick it up from .gitmodules,
which is inconsistent.

Teach "git commit" to pay attention to the setting in .gitmodules as
well.

Signed-off-by: Orgad Shaneh <orgads@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -1256,6 +1256,7 @@ int cmd_commit(int argc, const char **argv, const char *prefix)
 	struct wt_status s;
 
 	wt_status_prepare(&s);
+	gitmodules_config();
 	git_config(git_commit_config, &s);
 	in_merge = file_exists(git_path("MERGE_HEAD"));
 	s.in_merge = in_merge;