Introdude new Locks API, and the Forseti lock manager

 o The classic LockManager remains, but as an implementation of
   the new Locks API. It has been slightly improved to not contend
   on global data structures when taking locks it already holds.

   The classc lock manager is now referred to as the "Community
   Lock Manager".

 o Forseti is a new lock manager, available in enterprise only, it
   is faster than the community manager, and scales linearly as more
   execution threads are added. It uses a new deadlock detection
   scheme as well, which means deadlock detection is significantly
   faster and requires no pessimistic synchronization.