SERVER-13961 Remove thread-local write intents

This change makes all write intents go straight to the global write
intents list. Cleaning this up is necessary as a step to going to a
per-operation intents list, but it may cause more contention on the global
intents list.
SERVER-13961 Pass LockState to DBWrite and DBRead directly

This is part of the changes to move LockState be part of OperationContext
and not retrieved from TLS.