Introduce is_bare_repository() and core.bare configuration variable

This removes the old is_bare_git_dir(const char *) to ask if a
directory, if it is a GIT_DIR, is a bare repository, and
replaces it with is_bare_repository(void *).  The function looks
at core.bare configuration variable if exists but uses the old
heuristics: if it is ".git" or ends with "/.git", then it does
not look like a bare repository, otherwise it does.

Signed-off-by: Junio C Hamano <junkio@cox.net>

config.c

@@ -269,6 +269,11 @@ int git_default_config(const char *var, const char *value)
 		return 0;
 	}
 
+	if (!strcmp(var, "core.bare")) {
+		is_bare_repository_cfg = git_config_bool(var, value);
+		return 0;
+	}
+
 	if (!strcmp(var, "core.ignorestat")) {
 		assume_unchanged = git_config_bool(var, value);
 		return 0;