Keep '*' in pattern refspecs

Keep '*' in pattern refspecs

In order to do anything more capable with refspecs, the first step is
to keep the entire input. Additionally, validate patterns by checking
for the ref matching the rules for a pattern as given by
check_ref_format(). This requires a slight change to
check_ref_format() to make it enforce the requirement that the '*'
immediately follow a '/'.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>