gmi.c:
Allow NULL delivery_fn in gmi_join. This basically has no
effect but allows the processor to participate in multicasting
and membership.

BKrev: 40f419f8lTr8W134C7CXrtXRnzoMzw


git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@111 fd59a12c-fef9-0310-b244-a6a79926bd2f