BUG#28618 (Skipping into the middle of a group with SQL_SLAVE_SKIP_COUNTER

is possible):

When skipping the beginning of a transaction starting with BEGIN, the OPTION_BEGIN
flag was not set correctly, which caused the slave to not recognize that it was
inside a group. This patch sets the OPTION_BEGIN flag for BEGIN, COMMIT, ROLLBACK,
and XID events. It also adds checks if inside a group before decreasing the
slave skip counter to zero.

Begin_query_log_event was not marked that it could not end a group, which is now
corrected.


mysql-test/extra/rpl_tests/rpl_extraSlave_Col.test:
  Correcting slave skip counter to get the correct behaviour.
mysql-test/suite/rpl/r/rpl_slave_skip.result:
  Result change.
mysql-test/suite/rpl/t/rpl_slave_skip.test:
  Adding tests to check that skipping works for transactions:
  - Skipping one group with BEGIN first
  - Skipping two groups with BEGIN first
  - Skipping one group without BEGIN first but with AUTOCOMMIT=0
  - LOAD DATA INFILE under statement-based replication
mysql-test/suite/rpl_ndb/r/rpl_ndb_extraCol.result:
  Result change.
sql/log_event.cc:
  Adding checks if we're in a group when the slave skip counter is 1.
  In that case, we should keep going.
  
  Adding helping member function Log_event::continue_group() denoting
  that this event cannot end a group, and if the skip counter indicates
  that the group ends after this event, it should not decrease the skip
  counter.
  
  Query_log_event will change the OPTION_BEGIN flag for BEGIN, COMMIT, and
  ROLLBACK, even when skipping because of a positive skip count, and
  Xid_log_event will also affect the OPTION_BEGIN flag, even when being
  skipped.
  
  Begin_load_query_log_event cannot end a group, so it is marked to
  continue the group.
sql/log_event.h:
  Adding helper function Log_event::continue_group().
sql/rpl_rli.h:
  Adding Relay_log_info::get_flag() to get the value of a
  replication flag.
sql/slave.cc:
  Adding debug output and changing debug message.
mysql-test/suite/rpl/data/rpl_bug28618.dat:
  New BitKeeper file ``mysql-test/suite/rpl/data/rpl_bug28618.dat''
mysql-test/suite/rpl/t/rpl_slave_skip-slave.opt:
  New BitKeeper file ``mysql-test/suite/rpl/t/rpl_slave_skip-slave.opt''

mysql-test/suite/rpl_ndb/r/rpl_ndb_extraCol.result

@@ -707,7 +707,7 @@ Last_IO_Errno	#
 Last_IO_Error	#
 Last_SQL_Errno	1060
 Last_SQL_Error	Error 'Duplicate column name 'c6'' on query. Default database: 'test'. Query: 'ALTER TABLE t15 ADD COLUMN c6 INT AFTER c5'
-SET GLOBAL SQL_SLAVE_SKIP_COUNTER=2;
+SET GLOBAL SQL_SLAVE_SKIP_COUNTER=1;
 START SLAVE;
 *** Try to insert in master ****
 INSERT INTO t15 () VALUES(5,2.00,'Replication Testing',@b1,'Buda',2);