INT 15 U - DESQview v2.50+ - GET DISPLAY NAME
        AX = DE29h
        BX = 0004h
        CX = size of buffer in bytes
        DX = segment of window handle
        ES:DI -> buffer for display name
Return: CF clear if successful
            buffer filled with ASCIZ display name (truncated if necessary) or
              null string if no display
        CF set on error
Notes:  DESQview 2.50-2.52 are distributed as part of DESQview/X v1.0x.
        the name ":0" refers to the local display