Add exchange() & operator-- to LoggedAtomic<>
Add exchange() & operator-- to LoggedAtomic<>

Add some additional methods to LoggedAtomic which were missing
(compared to std::atomic).

Also fix operator++() to correctly return a T and not a reference.

Change-Id: Ia16e4999c548ee35593ada84efc2097effb11d73
Reviewed-on: http://review.couchbase.org/86583
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine