SERVER-5470 enable mongos plan cache commands in pass through mode.
SERVER-12136 fix explain asserts

Signed-off-by: Matt Kangas <matt.kangas@mongodb.com>
SERVER-12296 cache a backup plan for blocking sort solutions

Signed-off-by: Matt Kangas <matt.kangas@mongodb.com>
SERVER-11628: make sure ttl index is complete before deleting documents
SERVER-11595: move compact into Collection structure and do index bulk builds
SERVER-12247 Write commands allow un-indexable document to be replicated