WL#3056: Maria 2.0 Transactional and ACID Release

Overview of Maria Project Milestone 4 Tasks

transactions (w/o concurrency on indexes wl#3164)
recovery, albeit slow (without a checkpoint thread wl#3071, recovery may need to
read the log since the last daemon start)

When this milestone is complete, we have a releasable multi-user, MVCC and ACID
complient transactional storage engine. (Still missing some features and
optimizations)