- Don't call update_virtual_fields() if table->vfield is not set
- Don't prealloc memory for in open_tables() as this is very seldom used.


sql/records.cc:
  Don't call update_virtual_fields() if table->vfield is not set
sql/sql_base.cc:
  Don't prealloc memory for in open_tables() as this is very seldom used.
  Don't call update_virtual_fields() if table->vfield is not set
sql/sql_delete.cc:
  Don't call update_virtual_fields() if table->vfield is not set
sql/sql_handler.cc:
  Don't call update_virtual_fields() if table->vfield is not set
sql/sql_join_cache.cc:
  Don't call update_virtual_fields() if table->vfield is not set
  Move some frequent values to local variables
sql/sql_table.cc:
  Don't call update_virtual_fields() if table->vfield is not set
sql/sql_update.cc:
  Don't call update_virtual_fields() if table->vfield is not set
sql/table.cc:
  Assert if update_virtual_fields is called with wrong parameters