defineProperty is slow, don't use it for fastbuffer

lib/buffer.js

@@ -91,12 +91,8 @@ function Buffer (subject, encoding, offset) {
   // Are we slicing?
   if (typeof offset === 'number') {
     this.length = encoding;
-    Object.defineProperty(this, "parent", { enumerable: false,
-                                            value: subject, 
-                                            writable: false });
-    Object.defineProperty(this, "offset", { enumerable: false,
-                                            value: offset, 
-                                            writable: false });
+    this.parent = subject;
+    this.offset = offset;
   } else {
     // Find the length
     switch (type = typeof subject) {
@@ -120,22 +116,14 @@ function Buffer (subject, encoding, offset) {
 
     if (length > Buffer.poolSize) {
       // Big buffer, just alloc one.
-      var parent = new SlowBuffer(subject, encoding);
-      Object.defineProperty(this, "parent", { enumerable: false,
-                                              value: parent, 
-                                              writable: false });
-      Object.defineProperty(this, "offset", { enumerable: false,
-                                              value: 0, 
-                                              writable: false });
+      this.parent = new SlowBuffer(subject, encoding);
+      this.offset = 0;
+
     } else {
       // Small buffer.
       if (!pool || pool.length - pool.used < length) allocPool();
-      Object.defineProperty(this, "parent", { enumerable: false,
-                                              value: pool, 
-                                              writable: false });
-      Object.defineProperty(this, "offset", { enumerable: false,
-                                              value: pool.used, 
-                                              writable: false });
+      this.parent = pool;
+      this.offset = pool.used;
       pool.used   += length;
 
       // Do we need to write stuff?