SERVER-13562 limit and skip stages no longer return eof without calling work() on the child

Doing so could cause missing results for a tailable cursor.
SERVER-13561 Improve wire API message validation
SERVER-13579 Wait for deletion after migration in feature2.js
SERVER-13498 Get rid of LockStatus

This change removes all usages of LockStatus and pushes the lock
acquisitions to be inside the respective commands. This is a
refactoring on the way to per-document locking.