SERVER-14742 delete old explain and turn on explain 2.0
SERVER-15029: missing rename source field should be a no-op

(cherry picked from commit 8f8e59a78107a079c5367abdc31580d20428d9cc)
SERVER-13104 enumerate all possibilties for $or below an $and
SERVER-15118 While _rsConfig is synchronization type MX, _rsConfigState is type M.

Consulting _rsConfigState requires holding the mutex, even in executor context,
because _rsConfigState may be changed outside of executor context.
SERVER-14843: Fix mongosniff for decoding messages without a namespace
SERVER-5022 cleanup keypattern.h and shardkey.h, remove dead code
SERVER-15120 Early return from startReplication when no replication is enabled
SERVER-15130 Remove dead TopologyCoordinatorImpl::HeartbeatOptions class.
Merge with upstream/master