Add support for the node net module.

frog/samples/node/httpServer.dart

+#library('httpServer');
+
+#import('../../lib/node/node.dart');
+#import('../../lib/node/http.dart');
+
+void main() {
+  // Note: the callback function must use the actual types for the arguments,
+  // otherwise frog will strip out the type's methods.
+  http.createServer((ServerRequest req, ServerResponse res) {
+    res.writeHead(200, '', {'Content-Type': 'text/plain'});
+    res.end('Hello World\n');
+  }).listen(1337, "127.0.0.1");
+  console.log('Server running at http://127.0.0.1:1337/');
+}