Complementary patch since LOAD DATA INFILE was not covered in
the previous patch.

This patch adds a check so that the slave skip counter is not
decreased to zero if seeing a BEGIN_LOAD_QUERY_EVENT,
APPEND_BLOCK_EVENT, or CREATE_FILE_EVENT since these cannot
end a group. The group is terminated by an EXECUTE_LOAD_QUERY_
EVENT or DELETE_FILE_EVENT.


mysql-test/r/rpl_slave_skip.result:
  Result change.
mysql-test/t/rpl_slave_skip.test:
  Adding tests to test that the first event of a LOAD DATA INFILE
  can be skipped safely for both transactional and non-transactional
  tables. Also include a case that will generate a DELETE_FILE event
  last in the group, and this should be properly skipped as well.
sql/slave.cc:
  Not decrementing slave skip counter to zero when seeing a
  BEGIN_LOAD_QUERY_EVENT, APPEND_BLOCK_EVENT, or CREATE_FILE_EVENT
  since these cannot end a group.