change names of events to V2 from default

according to this post
http://dev.mysql.com/doc/internals/en/row-based-replication.html#rows-event
events are marked as version 0,1,2 (current) - the code had _V1 and no
version at all - I think it would b easier and morefuture compatible to
use V2 since it seems V3 is unavoidable.
Merge github.com:noplay/python-mysql-replication

Conflicts:
	pymysqlreplication/row_event.py
	pymysqlreplication/tests/test_basic.py
add support for null event and couple of new usages

nullevent is an event that can happen in the steam but we want to skip
it.

added two sample events like that: INTVAR_EVENT and GTID_LOG_EVENT -
those are events that happen when we do GTID enabled replication, but
are of no use (at least not for me at this time) in this packages
aspect. It might be when we support moving to a different master
seamlessly.
Merge github.com:noplay/python-mysql-replication

Conflicts:
	pymysqlreplication/constants/BINLOG.py
	pymysqlreplication/event.py
	pymysqlreplication/packet.py
re-adding gtid related events
Added comment about running tests
Added skipping notimplemented events to support GTID enabled env
disable reporting on non implemented events to help testing
removed type check that's no longer needed