This fixes a potential problem where, because of a config change, a joining
node may not have a previous fragment of a message. It now discards
continuations of that message until it is complete and a new message
arrives.

BKrev: 4203ea20pYSrD8ZyY3pxIHSXFSooeg


git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@475 fd59a12c-fef9-0310-b244-a6a79926bd2f