INT 15 - DESQview v2.20+ - SEND MESSAGE - "SETFLAGS" - SET OBJECT FLAGS
        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
                        bit 4: (DV/X) append messages with like status and
                                sender (stream-oriented mail)
                        bit 5: (DV/X) store mail in expanded memory (pool
                                grows as needed)
                        bit 6: (DV/X) make mailbox into non-owned mailbox
                if keyboard:
                        bit 5: exclusive input when keyboard in use for input
Return: nothing
Notes:  only available if the API level has been set to at least 2.20
        equivalent to performing SUBFROM and ADDTO calls on the object
        if a mailbox has bits 4 or 5 set, you must use "READINTO" rather than
          "READ" (see AH=12h/BX=1300h"READINTO") to retrieve messages
SeeAlso: AH=12h/BH=0Bh,AH=12h/BH=16h