message: Week beginning Monday time grain for MySQL
diff: @@ -139,6 +139,9 @@ class MySQLEngineSpec(BaseEngineSpec):
  "+ INTERVAL QUARTER({col}) QUARTER - INTERVAL 1 QUARTER"),
  Grain("year", _('year'), "DATE(DATE_SUB({col}, "
  "INTERVAL DAYOFYEAR({col}) - 1 DAY))"),
  + Grain("week_start_monday", _('week_start_monday'),
  + "DATE(DATE_SUB({col}, "
  + "INTERVAL DAYOFWEEK(DATE_SUB({col}, INTERVAL 1 DAY)) - 1 DAY))"),
  )
  @classmethod
  