Allow cluster mirrors to handle the absence of the checkpoint lib (libSaCkpt).

Allow cluster mirrors to handle the absence of the checkpoint lib (libSaCkpt).

The OpenAIS checkpoint library is going away; therefore, cmirrord must
operate without it.  The algorithms the handle the timing of when to send
a checkpoint, the determination of what to send, and which ongoing cluster
requests are relevent with respect to the checkpoints are unaffected.  We
need only replace the functions that actually perform the storing/transmitting
and retrieving/receiving of the checkpoint data.  Rather than store the
checkpoint data in an OpenAIS checkpoint file, we simply transmit it along
with the message that notifies the incoming node that the checkpoint is
ready.