* made unlzx able to read from stdin instead of files to support pipeing

   reason: just typeing:
   > lzx -r a PIPE:backup.lzx
   in an Amiga shell and
   > copy PIPE:backup.lzx SER:
   in another Amiga shell and
   > cat < /dev/ttyS0 | unlzx -x -c
   in the UNIX bash on the other side should make a real small but nice 
   backup system via serial cable. :o)