SERVER-12554 Lazily yield on count queries.

This avoids a regression when scanning a small set of documents.
SERVER-12702: add writeconcern operation option
SERVER-12707 clear lastOpTimeWritten when resyncing
SERVER-12607 allow update/delete write commands to be interrupted

Note that batch inserts are not interruptable, due to the way it is currently
handling CurOp objects.
SERVER-12089 Query planner: test exactly one text index for TEXT
SERVER-12702:clear data before running tests
Revert "SERVER-12089 Query planner: test exactly one text index for TEXT"

This reverts commit 263bc242b025553c54a5d1d926386b5ecebfc807.
SERVER-9765 use election time to resolve 2-primary situation, as a stopgap