FIX: signal-unregister bug

We now restore the default signal behavior when all listeners are
removed for a given signal.

Re-enabled test-signal-unregister

src/node.js

@@ -65,21 +65,48 @@ process.compile("(function (exports) {"
 // module.require("events");
 
 // Signal Handlers
+(function() {
+  var signalWatchers = {};
+    addListener = process.addListener,
+    removeListener = process.removeListener;
+
+  function isSignal (event) {
+    return event.slice(0, 3) === 'SIG' && process.hasOwnProperty(event);
+  };
+
+  // Wrap addListener for the special signal types
+  process.addListener = function (type, listener) {
+    var ret = addListener.apply(this, arguments);
+    if (isSignal(type)) {
+      if (!signalWatchers.hasOwnProperty(type)) {
+        var b = process.binding('signal_watcher'),
+          w = new b.SignalWatcher(process[type]);
+          w.callback = function () {
+            process.emit(type);
+          }
+        signalWatchers[type] = w;
+        w.start();
+      } else if (this.listeners(type).length === 1) {
+        signalWatchers[event].start();
+      }
+    }
+
+    return ret;
+  }
 
-function isSignal (event) {
-  return event.slice(0, 3) === 'SIG' && process.hasOwnProperty(event);
-};
+  process.removeListener = function (type, listener) {
+    var ret = removeListener.apply(this, arguments);
+    if (isSignal(type)) {
+      process.assert(signalWatchers.hasOwnProperty(type));
 
-process.addListener("newListener", function (event) {
-  if (isSignal(event) && process.listeners(event).length === 0) {
-    var b = process.binding('signal_watcher');
-    var w = new b.SignalWatcher(process[event]);
-    w.callback = function () {
-      process.emit(event);
-    };
-    w.start();
+      if (this.listeners(type).length === 0) {
+        signalWatchers[type].stop();
+      }
+    }
+
+    return ret;
   }
-});
+})();
 
 // Timers
 function addTimerListener (callback) {