# calls $func->($objid,$objtype,$fullrefname,$reftail);
# $reftail is RHS of ref after refs/\w+/
# breaks if $pattern matches any ref `refs/blah' where blah has no `/'
# calls $func->($objid,$objtype,$fullrefname,$reftail);
# $reftail is RHS of ref after refs/\w+/
# breaks if $pattern matches any ref `refs/blah' where blah has no `/'