Marking statements containing USER() or CURRENT_USER() as unsafe, causing
them to switch to using row-based logging in MIXED mode and generate a
warning in STATEMENT mode.


mysql-test/suite/rpl/r/rpl_switch_stm_row_mixed.result:
  Result change.
mysql-test/suite/rpl/t/rpl_switch_stm_row_mixed.test:
  Adding test to check that USER() and CURRENT_USER() cause a switch
  to row-based logging.
sql/sql_yacc.yy:
  Setting statements containing USER() or CURRENT_USER() to be unsafe.