Use defineProperty on prototype instead of __defineGetter__

This vastly improves performance by avoiding v8 tossing the
entire Reader object into the slow lookup path.

lib/ber/reader.js

@@ -24,18 +24,26 @@ function Reader(data) {
   // These hold the "current" state
   this._len = 0;
   this._offset = 0;
-
-  var self = this;
-  this.__defineGetter__('length', function() { return self._len; });
-  this.__defineGetter__('offset', function() { return self._offset; });
-  this.__defineGetter__('remain', function() {
-    return self._size - self._offset;
-  });
-  this.__defineGetter__('buffer', function() {
-    return self._buf.slice(self._offset);
-  });
 }
 
+Object.defineProperty(Reader.prototype, 'length', {
+  enumerable: true,
+  get: function () { return (this._len); }
+});
+
+Object.defineProperty(Reader.prototype, 'offset', {
+  enumerable: true,
+  get: function () { return (this._offset); }
+});
+
+Object.defineProperty(Reader.prototype, 'remain', {
+  get: function () { return (this._size - this._offset); }
+});
+
+Object.defineProperty(Reader.prototype, 'buffer', {
+  get: function () { return (this._buf.slice(this._offset)); }
+});
+
 
 /**
  * Reads a single byte and advances offset; you can pass in `true` to make this

lib/ber/writer.js

@@ -50,16 +50,16 @@ function Writer(options) {
   // A list of offsets in the buffer where we need to insert
   // sequence tag/len pairs.
   this._seq = [];
-
-  var self = this;
-  this.__defineGetter__('buffer', function() {
-    if (self._seq.length)
-      throw new InvalidAsn1Error(self._seq.length + ' unended sequence(s)');
-
-    return self._buf.slice(0, self._offset);
-  });
 }
 
+Object.defineProperty(Writer.prototype, 'buffer', {
+  get: function () {
+    if (this._seq.length)
+      throw new InvalidAsn1Error(this._seq.length + ' unended sequence(s)');
+
+    return (this._buf.slice(0, this._offset));
+  }
+});
 
 Writer.prototype.writeByte = function(b) {
   if (typeof(b) !== 'number')