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''

sql/rpl_rli.h

@@ -365,6 +365,18 @@ public:
     m_flags |= (1UL << flag);
   }
 
+  /**
+     Get the value of a replication state flag.
+
+     @param flag Flag to get value of
+
+     @return @c true if the flag was set, @c false otherwise.
+   */
+  bool get_flag(enum_state_flag flag)
+  {
+    return m_flags & (1UL << flag);
+  }
+
   /**
      Clear the value of a replication state flag.