files

NOTE: this is the backport to next-mr.
            
SHOW BINLOG EVENTS does not work with relay log files. If issuing
"SHOW BINLOG EVENTS IN 'relay-log.000001'" in a non-empty relay
log file (relay-log.000001), mysql reports empty set.
            
This patch addresses this issue by extending the SHOW command
with RELAYLOG. Events in relay log files can now be inspected by
issuing SHOW RELAYLOG EVENTS [IN 'log_name'] [FROM pos] [LIMIT
[offset,] row_count].

mysql-test/extra/rpl_tests/rpl_show_relaylog_events.inc:
  Shared part of the test case.
mysql-test/include/show_binlog_events.inc:
  Added options $binary_log_file, $binary_log_limit_row, 
  $binary_log_limit_offset so that show_binlog_events can take 
  same parameters as SHOW BINLOG EVENTS does.
mysql-test/include/show_relaylog_events.inc:
  Clone of show_binlog_events for relaylog events.
mysql-test/suite/rpl/t/rpl_row_show_relaylog_events.test:
  Test case for row based replication.
mysql-test/suite/rpl/t/rpl_stm_mix_show_relaylog_events.test:
  Test case for statement and mixed mode replication.
sql/lex.h:
  Added RELAYLOG symbol.
sql/mysqld.cc:
  Added "show_relaylog_events" to status_vars.
sql/sp_head.cc:
  Set SQLCOM_SHOW_RELAYLOG_EVENTS to return flags=
  sp_head::MULTI_RESULTS; in sp_get_flags_for_command as
  SQLCOM_SHOW_BINLOG_EVENTS does.
sql/sql_lex.h:
  Added sql_command SQLCOM_SHOW_RELAYLOG_EVENTS to lex enum_sql_command.
sql/sql_parse.cc:
  Added handling of SQLCOM_SHOW_RELAYLOG_EVENTS.
sql/sql_repl.cc:
  mysql_show_binlog_events set to choose the log file to use based on
  the command issued (SHOW BINLOG|RELAYLOG EVENTS).
sql/sql_yacc.yy:
  Added RELAYLOG to the grammar.