process: fix regression in unlistening signals

process: fix regression in unlistening signals

When the last signal listener is removed, the signal wrap should be
closed, restoring the default signal handling behaviour. This is done in
a (patched) process.removeListener(). However, events.removeAllListeners
has an optimization to avoid calling removeListener() if there are no
listeners for the 'removeListener' event, introduced in 56668f54d1. That
caused the following code to fail to terminate:

    process.stdin.resume();
    function listener() {};
    process.on('SIGINT', listener);
    process.removeAllListeners('SIGINT');
    process.kill(process.pid, 'SIGINT')

while the following will terminate:

    process.stdin.resume();
    function listener() {};
    process.on('SIGINT', listener);
    process.removeListener('SIGINT', listener);
    process.kill(process.pid, 'SIGINT')

Replace the method patching with use of the 'newListener' and
'removeListener' events, which will fire no matter which methods are
used to add or remove listeners.

PR-URL: https://github.com/iojs/io.js/pull/687
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>