Add remote.<name>.proxy

As well as allowing a default http.proxy option, allow it to be set
per-remote.

Signed-off-by: Sam Vilain <sam.vilain@catalyst.net.nz>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.c

@@ -278,6 +278,8 @@ static int handle_config(const char *key, const char *value)
 	} else if (!strcmp(subkey, ".tagopt")) {
 		if (!strcmp(value, "--no-tags"))
 			remote->fetch_tags = -1;
+	} else if (!strcmp(subkey, ".proxy")) {
+		remote->http_proxy = xstrdup(value);
 	}
 	return 0;
 }