Comment 68 for bug 73536

Here's a revised version of the SignalPipeWatcher patch.

* SIGTERM/SIGINT/SIGHUP all do a graceful exit. I tested Chromium, VLC and GIMP using strace with these signals and they all exit normally returning exit codes and not signals.

* SignalPipeWatcher does not chain to previous handler and registers after nsProfileLock so it takes over for these signals. The nsProfileLock signal handler is unwanted since we are doing a normal exit which unlocks the profile in the destructor.

* After the first termination attempt the previous handler is restored so subsequent attempts can unlock the profile and kill the process immediately like before.