SERVER-16201 Create replica set downgrade test.
SERVER-15541 preserve chunk ranges during long-running yielding count/geoNear
SERVER-15541 restore yielding per-document to the filemd5 command
SERVER-16058 change misleading message about cursor cleanup in parallel.cpp
SERVER-16190 Add hasFailed() function to JSThreadConfig.

Allows the caller to detect if the JSThread has thrown a JS or C++
exception, without calling join() on the thread.
SERVER-16072 improve namespace construction in commands
SERVER-16183: drop queued kv idents at startup
SERVER-16171: fix repairIterator releasing under WT
SERVER-16078 SERVER-15945: consolidate WriteConflictException logging and do backoff
Merge remote-tracking branch 'upstream/master'