buffer: improve Buffer constructor

Increase the performance of new Buffer construction by initializing all
properties before SetIndexedPropertiesToExternalArrayData call.

Reviewed-by: Trevor Norris <trev.norris@gmail.com>

lib/buffer.js

@@ -66,6 +66,7 @@ function Buffer(subject, encoding) {
                          'size: 0x' + kMaxLength.toString(16) + ' bytes');
   }
 
+  this.parent = null;
   if (this.length <= (Buffer.poolSize >>> 1) && this.length > 0) {
     if (this.length > poolSize - poolOffset)
       createPool();
@@ -217,11 +218,6 @@ Buffer.byteLength = function(str, enc) {
 };
 
 
-// pre-set for values that may exist in the future
-Buffer.prototype.length = undefined;
-Buffer.prototype.parent = undefined;
-
-
 // toString(encoding, start=0, end=buffer.length)
 Buffer.prototype.toString = function(encoding, start, end) {
   var loweredCase = false;