* syscalls.cc (setsid): Detach process from its console if the current

controlling tty is the console and already closed.
* dtable.h (class dtable): Add members to count descriptors referring to the
console.
* dtable.cc (dtable::dec_console_fds): New function to detach process from its
console.
(dtable::release): Decrement the counter of console descriptors.
(dtable::build_fhandler): Increment it.
* exception.cc (ctrl_c_handler): Send SIGTERM to myself when catch
CTRL_SHUTDOWN_EVENT.

winsup/cygwin/syscalls.cc

@@ -240,6 +240,8 @@ setsid (void)
   /* FIXME: for now */
   if (myself->pgid != _getpid ())
     {
+      if (myself->ctty == TTY_CONSOLE && !cygheap->fdtab.has_console_fds ())
+	FreeConsole ();
       myself->ctty = -1;
       myself->sid = _getpid ();
       myself->pgid = _getpid ();