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>