Set flags

        Entry:
          AH = 12h
          BH = 15h
          BL = object
               00h DWORD on top of stack
                   Mailbox, keyboard, or pointer only
               02h mailbox for task whose handle is on top of stack
               03h mailbox for current task
               04h keyboard for task whose handle is on top of stack
               05h keyboard for current task
          STACK: DWORD flags
                  If mailbox:
                          Bit 0: all mail messages in common memory
                          Bit 1: allow write even if closed
                          Bit 2: don't erase messages when mailbox closed
                  If keyboard:
                          Bit 5: exclusive input when keyboard in use for input

        Return:
          Nothing

        Note:   This call is only available if the API level has been
        set to at least 2.2