INT 2F U - TRAP.COM - INSTALLATION CHECK
        AX = DA55h
        DL = interrupt number
        DH = ???
Return: if installed
            AH = interrupt number
            AL = ???
            ES:BX -> ???
Notes:  TRAP is an interrupt call tracer by Patrick Phillipot/Udo Chrosziel
        a separate copy of TRAP is loaded for each interrupt to be traced; thus
          the interrupt number is part of the installation check