Improve fatal messages in raft

Change-Id: I4ebdb9d3bd0ace23f921556e57174b2ee27f9627
Merge branch 'master' of github.com:soheilhy/beehive
state: Add HasEmptyTx to Transactional

Change-Id: I9d835a46fcfb037215e85a2f13a7636c81be5ff3
core: mirco-optimization for empty L2 transactions

When there is no state update in a L2 transaction we can sometimes
directly emit L2 messages. This will improve the performance of sync
by 10%.

Change-Id: If1c5868182180dd60de1b3da460ac839d065c6a4