Add the --multiple option to specify that all arguments are either
groups or remotes. The primary reason for adding this option is
to allow us to re-implement 'git remote update' using fetch.
It would have been nice if this option was not needed, but since
the colon in a refspec is optional, it is in general not possible
to know whether a single, colon-less argument is a remote or a
refspec.
Signed-off-by: Björn Gustavsson <bgustavsson@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>