SERVER-15527 add more execution stats to explain
SERVER-15662 temporarily disable HBReconfigDuringReconfigFails
SERVER-15535 When using replSetFreeze to end a stepDown period, make sure single node replsets become PRIMARY again
SERVER-15535 Clear sharding state on stepdown
SERVER-15535 Rename sharding_state_after_reconfig.js to sharding_state_after_stepdown.js
SERVER-15535 Ensure that a node in a single node replica set will become PRIMARY when its stepdown period ends
SERVER-15527 OpCtx no longer needs to be passed into explainStages
SERVER-15528 Refactor DistinctScan to do less in each work() call
SERVER-15198: Make scramIterationCount user configurable
SERVER-15402 Improve ShardPtr/ConnectionString management for commands and setVersion

Make Shard almost logically immutable. The only non-const method remaining is reset(), which will eventually be removed.
SERVER-15535 refactor jstests/replsets/rollback_auth.js to no longer use replSetBlind
SERVER-15535 remove last vestiges of replSetBlind
SERVER-15638 Wake up SyncSourceFeedback thread when we find a new sync source
SERVER-15535 Break cancel deadlock in ReplicationExecutor.
SERVER-15535 Unit test for single node replica sets becoming PRIMARY when stepdown period ends
SERVER-15523 cleanup initial connection in Config::reloadSettings
SERVER-15591  enforce secondaryThrottle during moveChunk commit
SERVER-15535 replication logic fixes for replsets_priority1.js

During parsing of a replSetUpdatePosition command, a node should not allow any updates
to move a particular node's optime back in time. Previously, we were allowing updates to
go back in time if they were updates for the node itself -- this breaks if you hear a stale
update via remote nodes for yourself.  Updates to our own lastOpApplied are allowed to go back
in time if the update's source is from ourselves.

Also, during spanning tree formation, we should only connect to nodes that are strictly
ahead of us, even if they are in state PRIMARY.  This is because node state is transient
and our knowledge of it may be out-of-date.

These two behavior changes should fix replsets_priority1.js for new replset impl.
SERVER-15535 comment edit
SERVER-15535 enhance freshness checker to consider priorities as well.