ldr now sends Option<AEReq> to peer handlers rather than ~str
ldr now sends Option<AEReq> to peer handlers rather than ~str

This is in preparation for the peer handlers managing the hearbeat
timeouts.  They will use the information from the last AEReq (with
entries) from the leader to know how to set the AEReq to send to the
follower.

lenary/cs4414-project