SERVER-15535 Perform better error detection in stepdown.js
SERVER-15535 Use heartbeat progress to wait for secondaries to catch up before stepping down.

Only when processing heartbeat data do we know both that a secondary is caught up
and that it is electable, which are the prerequisites to a step down.
SERVER-15736 remove disabled replication tests
SERVER-15716 change logical not to bitwise not in NetworkInterfaceMock
SERVER-15535 clear sleptLastElection flag after election is over
SERVER-15535 avoid negative buffer stats
assert codes
SERVER-15717 Fix use-after-free when logging at high log levels in replication network interface.
Revert "SERVER-15535 clear sleptLastElection flag after election is over"

This reverts commit 80ea7a136358ae0c9533feda29a2758ba063ef81.
Merge remote-tracking branch 'upstream/master'