SERVER-15535 On force reconfig, bump the supplied config version by a large-ish random number.

This is for consistency with the legacy implementation, and to increase the
likelihood that if several nodes take force reconfigs, the nodes recognize them
to be different configurations, and choose one as the winner.
SERVER-15535 Close all connections when removed from a replica set.

Also, do not dassert if a node receives a position update for a RBID for which
it has no handshake information.  This can legitimately happen if the sender of
the handshake hasn't yet noticed that it has been removed from the replica set.