Merge branch 'ds/midx-normalize-pathname-before-comparison'

The path taken by "git multi-pack-index" command from the end user
was compared with path internally prepared by the tool withut first
normalizing, which lead to duplicated paths not being noticed,
which has been corrected.

* ds/midx-normalize-pathname-before-comparison:
  cache: use const char * for get_object_directory()
  multi-pack-index: use --object-dir real path
  midx: use real paths in lookup_multi_pack_index()

environment.c

@@ -273,7 +273,7 @@ const char *get_git_work_tree(void)
 	return the_repository->worktree;
 }
 
-char *get_object_directory(void)
+const char *get_object_directory(void)
 {
 	if (!the_repository->objects->odb)
 		BUG("git environment hasn't been setup");