hen using GTIDs and semi sync, whenever a transaction is
executed on the master but is not sent to the slave because it
already has this id, semi sync will time out.  In fact, semi sync
hooks will still trigger a waiting process in the master, but as
the transaction never reaches the slave, a reply is never sent.

Making the semi sync plug-in call the reportReplyBinlog method
whenever a transaction is skipped solves this issue.

@semisync_master.cc
  A new method skipSlaveReply was created  to allow
  the interruption of the waiting process without a reply.
@semisync_master.h
  New method header and other headers updated
@semisync_master_plugin.cc
  The after send event response now depends on the transaction being 
  skipped or not
@replication.h rpl_handler.h rpl_handler.cc
  The after_send_event hook now takes new parameters that flag if the
  event was skipped, what was is position and binlog. 
@rpl_master.cc
  The after_send_event hook is now always invoked taking as new
  parameters the position and binlog when transactions are skipped.