Add duration timer support.
ckpt.h:
Add retained checkpoints timer to checkpoint structure.
ckpt.c:
Add retained checkpoints while also cleaning up memory leakage that occurs
because of a lack of retained events.

BKrev: 414f7d20vmWMyWW9eWJST5Ew5sw_yw


git-svn-id: http://svn.fedorahosted.org/svn/corosync/trunk@273 fd59a12c-fef9-0310-b244-a6a79926bd2f