Fixes to RedisBagOStuff

* Avoid serializing scalars like the memcached client does.
  This means incr/decr can be fast and preserve the TTL.
* Properly call unwatch() in the cas() method.
* Made the expiry set on add() actually atomic.
* Also cleaned up the profiling calls.

bug: 56069
Change-Id: I3e0d1c4888062544c54aef32085f8ce608ff5423
Merge "Fixes to RedisBagOStuff"