windows: don't blow when a signal handler is attached

Blowing up when the user attaches a signal handler makes no sense. Also,
in Node 0.10 signals will be supported, so allow people to get used to
it.

src/node.js

@@ -462,6 +462,10 @@
   };
 
   startup.processSignalHandlers = function() {
+    // Not supported on Windows.
+    if (process.platform === 'win32')
+      return;
+
     // Load events module in order to access prototype elements on process like
     // process.addListener.
     var signalWatchers = {};