xterm:  DISPLAY is not set
######### Forked, but do not know how to create a new TTY. #########
  Since two debuggers fight for the same TTY, input is severely entangled.

  I know how to switch the output to a different window in xterms
  and OS/2 consoles only.  For a manual switch, put the name of the created TTY
  in $DB::fork_TTY, or define a function DB::get_fork_TTY() returning this.

  On UNIX-like systems one can get the name of a TTY for the given window
  by typing tty, and disconnect the shell from TTY by sleep 1000000.