ckpt.c:
defect 629
Return error if checkpoint has been unlinked on retentation duration set

BKrev: 42b3192dcHnUOXNAKirryjp4WHDl9g


git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@677 fd59a12c-fef9-0310-b244-a6a79926bd2f