Merge branch 'mh/ref-api-lazy-loose'

Refs API is updated to lazily read sub-hierarchies of refs/ namespace,
so that we do not have to grab everything from the filesystem when we
are only interested in listing branches, for example.

By Michael Haggerty (17) and Junio C Hamano (1)
* mh/ref-api-lazy-loose:
  refs: fix find_containing_dir() regression
  refs: read loose references lazily
  read_loose_refs(): eliminate ref_cache argument
  struct ref_dir: store a reference to the enclosing ref_cache
  search_for_subdir(): return (ref_dir *) instead of (ref_entry *)
  get_ref_dir(): add function for getting a ref_dir from a ref_entry
  read_loose_refs(): rename function from get_ref_dir()
  refs: wrap top-level ref_dirs in ref_entries
  find_containing_dir(): use strbuf in implementation of this function
  bisect: copy filename string obtained from git_path()
  do_for_each_reflog(): use a strbuf to hold logfile name
  do_for_each_reflog(): return early on error
  get_ref_dir(): take the containing directory as argument
  refs.c: extract function search_for_subdir()
  get_ref_dir(): require that the dirname argument ends in '/'
  get_ref_dir(): rename "base" parameter to "dirname"
  get_ref_dir(): use a strbuf to hold refname
  get_ref_dir(): return early if directory cannot be read

bisect.c

@@ -833,7 +833,7 @@ static int check_ancestors(const char *prefix)
  */
 static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 {
-	const char *filename = git_path("BISECT_ANCESTORS_OK");
+	char *filename = xstrdup(git_path("BISECT_ANCESTORS_OK"));
 	struct stat st;
 	int fd;
 
@@ -842,11 +842,11 @@ static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 
 	/* Check if file BISECT_ANCESTORS_OK exists. */
 	if (!stat(filename, &st) && S_ISREG(st.st_mode))
-		return;
+		goto done;
 
 	/* Bisecting with no good rev is ok. */
 	if (good_revs.nr == 0)
-		return;
+		goto done;
 
 	/* Check if all good revs are ancestor of the bad rev. */
 	if (check_ancestors(prefix))
@@ -859,6 +859,8 @@ static void check_good_are_ancestors_of_bad(const char *prefix, int no_checkout)
 			filename, strerror(errno));
 	else
 		close(fd);
+ done:
+	free(filename);
 }
 
 /*