check_repository_format_gently: stop using git_config_early

There's a chicken-and-egg problem with using the regular
git_config during the repository setup process. We get
around it here by using a special interface that lets us
specify the per-repo config, and avoid calling
git_pathdup().

But this interface doesn't actually make sense. It will look
in the system and per-user config, too; we definitely would
not want to accept a core.repositoryformatversion from
there.

The git_config_from_file interface is a better match, as it
lets us look at a single file.

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

setup.c

@@ -409,15 +409,10 @@ static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 	repo_config = sb.buf;
 
 	/*
-	 * git_config() can't be used here because it calls git_pathdup()
-	 * to get $GIT_CONFIG/config. That call will make setup_git_env()
-	 * set git_dir to ".git".
-	 *
-	 * We are in gitdir setup, no git dir has been found useable yet.
-	 * Use a gentler version of git_config() to check if this repo
-	 * is a good one.
+	 * Ignore return value; for historical reasons, we must treat a missing
+	 * config file as a noop (git-init relies on this).
 	 */
-	git_config_early(fn, NULL, repo_config);
+	git_config_from_file(fn, repo_config, NULL);
 	if (GIT_REPO_VERSION_READ < repository_format_version) {
 		if (!nongit_ok)
 			die ("Expected git repo version <= %d, found %d",