setup_git_env: use git_pathdup instead of xmalloc + sprintf

This is shorter, harder to get wrong, and more clearly
captures the intent.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

environment.c

@@ -135,15 +135,11 @@ static void setup_git_env(void)
 	gitfile = read_gitfile(git_dir);
 	git_dir = xstrdup(gitfile ? gitfile : git_dir);
 	git_object_dir = getenv(DB_ENVIRONMENT);
-	if (!git_object_dir) {
-		git_object_dir = xmalloc(strlen(git_dir) + 9);
-		sprintf(git_object_dir, "%s/objects", git_dir);
-	}
+	if (!git_object_dir)
+		git_object_dir = git_pathdup("objects");
 	git_index_file = getenv(INDEX_ENVIRONMENT);
-	if (!git_index_file) {
-		git_index_file = xmalloc(strlen(git_dir) + 7);
-		sprintf(git_index_file, "%s/index", git_dir);
-	}
+	if (!git_index_file)
+		git_index_file = git_pathdup("index");
 	git_graft_file = getenv(GRAFT_ENVIRONMENT);
 	if (!git_graft_file)
 		git_graft_file = git_pathdup("info/grafts");