Open object

        Entry:
          AH = 12h
          BH = 0Ch
          BL = object
               00h handle is DWORD on top of stack
                   Window:   fill with given character
                   Keyboard: attach to a window
                   Timer:         open
                   Pointer:  start taking input for window
                   Panel:         associate with a panel file
               01h fill task's default window with given character
               02h open given task's mailbox for input
                   (task's handle on stack)
               03h open current task's mailbox
               04h attach a KEYBOARD to a window (handle on top of stack)
               05h attach task's default KEYBOARD to a window
               06h open a task's OBJECTQ (task's handle on top of stack)
               07h open current task's OBJECTQ
           STACK: (if window)   DWORD character to fill with
                  (if keyboard) DWORD handle of window to attach to
                  (if pointer)  DWORD handle of window to attach to
                  (if panel)    DWORD length of filename
                                DWORD address of filename
                  (otherwise)   nothing

        Notes:  Special action taken if first byte of panel file name
                is 1Bh if first two bytes of panel file "name" are C0hC3h,
                then the "name" IS the panel file result code of open
                may be retrieved with STATUS message