Async open and subscribe needed to check for registered call back
functions and retrun an error if there were no assocated callbacks.

BKrev: 42483e43sOS_W8zCqoAZNHTy43FhkA


git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@552 fd59a12c-fef9-0310-b244-a6a79926bd2f