(Old code failed for INSERT ... ON DUPLICATE with prepared statements) 
Instead, always reset table->insert_values on open.


mysql-test/t/trigger.test:
  Fix test for --ps-protocol
sql/sql_base.cc:
  Clear insert_values on open_table
sql/sql_insert.cc:
  Remove clear_insert_values()
sql/sql_parse.cc:
  Remove clear_insert_values()
sql/sql_prepare.cc:
  Remove clear_insert_values()
sql/table.cc:
  Remove clear_insert_values()
sql/table.h:
  Remove clear_insert_values()