Refactored the code to make the Log events to go through a cache before
being written to the binary log. In particular, after the WL#2687 only
Query Log Events with DDLS, BEGIN, COMMIT and ROLLBACK, Incident Events
and Rotate Events were written directly to the binary log without
going through a cache.

After this WL, only Incident Events and Rotate Events are still written
directly to the binary log.