INT 2F - DESQview v2.26+ XDI - CUSTOM SUBFUNCTION, Ralf Brown's XDI drivers
AX = DE01h
BX = 5242h ("RB")
CX:DX = program identifier
656F7000h ("eop",0) for DVeop
Return: AX = 5242h ("RB") if installed
ES:BX -> data or entry point (see #03100)
CX = version number (CH = major, CL = minor)