Define $DB::fork_TTY

Error:
  DB<1> Debugged program terminated.  Use q to quit or R to restart,
  use O inhibit_exit to avoid stopping after program termination,
  h q, h R or h O to get additional info.
######### Forked, but do not know how to change a TTY. #########
  Define $DB::fork_TTY
       - or a function DB::get_fork_TTY() which will set $DB::fork_TTY.
  The value of $DB::fork_TTY should be the name of TTY to use.
  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.

Cause
when a process is forked the program does not know which tty to use

Solution:
set  $DB::fork_TTY = 0;
set the tty for child = 0 or any particular tty you want to use