After review and after merge fixes.


mysql-test/t/trigger.test:
  After merge fix. Updated error codes.
sql/sp_head.cc:
  After merge fix.
  To give some chances for functions/triggers we have to close tables during sp_instr_* 
  execution only if we have opened them before.
sql/sp_head.h:
  After merge fix. sp_instr constructor now takes one more argument.
sql/sql_trigger.cc:
  After merge and review fixes.
  Some variable renaming and optimizations.
sql/sql_yacc.yy:
  After merge fixes.
  sp_instr_* classes now require sp context as constructor parameter.
  Also we should be careful with adding table for which we are creating trigger to table 
  list. Some elements in trigger body can damage LEX::query_tables and so we should add this
  table to list only after parsing trigger body.