Mark http-fetch without -a as deprecated

As the use of http-fetch without -a can create an object store that is
invalid to the point where it cannot even be fsck'd, mark it as
deprecated.  A future release should change the default and then
remove the option entirely.

Signed-off-by: Ben Walton <bwalton@artsci.utoronto.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http-fetch.c

@@ -56,6 +56,10 @@ int main(int argc, const char **argv)
 		commits = 1;
 	}
 
+	if (get_all == 0)
+		warning("http-fetch: use without -a is deprecated.\n"
+			"In a future release, -a will become the default.");
+
 	if (argv[arg])
 		str_end_url_with_slash(argv[arg], &url);