* (os-job-control?): New primitive tells the runtime system whether or

* (os-job-control?): New primitive tells the runtime system whether or
  not the operating system supports job control.  This is needed when
  hacking subprocesses.

* (open-pty-master): Close the channel if allocation forces GC.

* (pty-master-kill, pty-master-stop, pty-master-continue,
  pty-master-interrupt, pty-master-quit): New primitives to send
  standard signals down a PTY master.