remote: New function remote_is_configured()

Previously, there was no easy way to check for the existence of a
configured remote. remote_get for example would always create the remote
"on demand".

This new function returns 1 if the remote is configured, 0 otherwise.

Signed-off-by: Finn Arne Gangstad <finnag@pvv.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.h

@@ -45,6 +45,7 @@ struct remote {
 };
 
 struct remote *remote_get(const char *name);
+int remote_is_configured(const char *name);
 
 typedef int each_remote_fn(struct remote *remote, void *priv);
 int for_each_remote(each_remote_fn fn, void *priv);