repository.c: replace hold_locked_index() with repo_hold_locked_index()

hold_locked_index() assumes the index path at $GIT_DIR/index. This is
not good for places that take an arbitrary index_state instead of
the_index, which is basically everywhere except builtin/.

Replace it with repo_hold_locked_index(). hold_locked_index() remains
as a wrapper around repo_hold_locked_index() to reduce changes in builtin/

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

repository.c

@@ -3,6 +3,7 @@
 #include "object-store.h"
 #include "config.h"
 #include "object.h"
+#include "lockfile.h"
 #include "submodule-config.h"
 
 /* The main repository */
@@ -263,3 +264,12 @@ int repo_read_index(struct repository *repo)
 
 	return read_index_from(repo->index, repo->index_file, repo->gitdir);
 }
+
+int repo_hold_locked_index(struct repository *repo,
+			   struct lock_file *lf,
+			   int flags)
+{
+	if (!repo->index_file)
+		BUG("the repo hasn't been setup");
+	return hold_lock_file_for_update(lf, repo->index_file, flags);
+}