Instead of looking on the filesystem inside ".git/refs/remotes/origin",
use "git for-each-ref" to check for leftover references under the
remote's old name.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Reviewed-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>