Some small optimizations

lib/http.js

@@ -825,7 +825,9 @@ ServerResponse.prototype.writeHead = function(statusCode) {
 
     } else {
       // handle object case
-      for (var k in obj) {
+      var keys = Object.keys(obj);
+      for (var i = 0; i < keys.length; i++) {
+        var k = keys[i];
         if (k) headers[k] = obj[k];
       }
     }

lib/net_uv.js

@@ -371,18 +371,13 @@ Socket.prototype.write = function(data, arg1, arg2) {
 
   // parse arguments
   if (arg1) {
-    switch (typeof arg1) {
-      case 'string':
-        encoding = arg1;
-        cb = arg2;
-        break;
-
-      case 'function':
-        cb = arg1;
-        break;
-
-      default:
-        throw new Error("bad arg");
+    if (typeof arg1 === 'string') {
+      encoding = arg1;
+      cb = arg2;
+    } else if (typeof arg1 === 'function') {
+      cb = arg1;
+    } else {
+      throw new Error("bad arg");
     }
   }