buffer: make SlowBuffer inherit from Buffer

This frees us from manually having to copy over functions to SlowBuffer's
prototype (which has bitten us multiple times in the past).

As an added bonus, the `inspect()` function is now shared between Buffer
and SlowBuffer, removing some duplicate code.

Closes #3228.

lib/buffer.js

@@ -33,6 +33,10 @@ function binaryWarn() {
 
 exports.INSPECT_MAX_BYTES = 50;
 
+// Make SlowBuffer inherit from Buffer.
+// This is an exception to the rule that __proto__ is not allowed in core.
+SlowBuffer.prototype.__proto__ = Buffer.prototype;
+
 
 function toHex(n) {
   if (n < 16) return '0' + n.toString(16);
@@ -40,20 +44,6 @@ function toHex(n) {
 }
 
 
-SlowBuffer.prototype.inspect = function() {
-  var out = [],
-      len = this.length;
-  for (var i = 0; i < len; i++) {
-    out[i] = toHex(this[i]);
-    if (i == exports.INSPECT_MAX_BYTES) {
-      out[i + 1] = '...';
-      break;
-    }
-  }
-  return '<SlowBuffer ' + out.join(' ') + '>';
-};
-
-
 SlowBuffer.prototype.hexSlice = function(start, end) {
   var len = this.length;
 
@@ -302,24 +292,25 @@ function allocPool() {
 
 // Static methods
 Buffer.isBuffer = function isBuffer(b) {
-  return b instanceof Buffer || b instanceof SlowBuffer;
+  return b instanceof Buffer;
 };
 
 
 // Inspect
 Buffer.prototype.inspect = function inspect() {
   var out = [],
-      len = this.length;
+      len = this.length,
+      name = this.constructor.name;
 
   for (var i = 0; i < len; i++) {
-    out[i] = toHex(this.parent[i + this.offset]);
+    out[i] = toHex(this[i]);
     if (i == exports.INSPECT_MAX_BYTES) {
       out[i + 1] = '...';
       break;
     }
   }
 
-  return '<Buffer ' + out.join(' ') + '>';
+  return '<' + name  + ' ' + out.join(' ') + '>';
 };
 
 
@@ -1143,32 +1134,3 @@ Buffer.prototype.writeDoubleLE = function(value, offset, noAssert) {
 Buffer.prototype.writeDoubleBE = function(value, offset, noAssert) {
   writeDouble(this, value, offset, true, noAssert);
 };
-
-SlowBuffer.prototype.readUInt8 = Buffer.prototype.readUInt8;
-SlowBuffer.prototype.readUInt16LE = Buffer.prototype.readUInt16LE;
-SlowBuffer.prototype.readUInt16BE = Buffer.prototype.readUInt16BE;
-SlowBuffer.prototype.readUInt32LE = Buffer.prototype.readUInt32LE;
-SlowBuffer.prototype.readUInt32BE = Buffer.prototype.readUInt32BE;
-SlowBuffer.prototype.readInt8 = Buffer.prototype.readInt8;
-SlowBuffer.prototype.readInt16LE = Buffer.prototype.readInt16LE;
-SlowBuffer.prototype.readInt16BE = Buffer.prototype.readInt16BE;
-SlowBuffer.prototype.readInt32LE = Buffer.prototype.readInt32LE;
-SlowBuffer.prototype.readInt32BE = Buffer.prototype.readInt32BE;
-SlowBuffer.prototype.readFloatLE = Buffer.prototype.readFloatLE;
-SlowBuffer.prototype.readFloatBE = Buffer.prototype.readFloatBE;
-SlowBuffer.prototype.readDoubleLE = Buffer.prototype.readDoubleLE;
-SlowBuffer.prototype.readDoubleBE = Buffer.prototype.readDoubleBE;
-SlowBuffer.prototype.writeUInt8 = Buffer.prototype.writeUInt8;
-SlowBuffer.prototype.writeUInt16LE = Buffer.prototype.writeUInt16LE;
-SlowBuffer.prototype.writeUInt16BE = Buffer.prototype.writeUInt16BE;
-SlowBuffer.prototype.writeUInt32LE = Buffer.prototype.writeUInt32LE;
-SlowBuffer.prototype.writeUInt32BE = Buffer.prototype.writeUInt32BE;
-SlowBuffer.prototype.writeInt8 = Buffer.prototype.writeInt8;
-SlowBuffer.prototype.writeInt16LE = Buffer.prototype.writeInt16LE;
-SlowBuffer.prototype.writeInt16BE = Buffer.prototype.writeInt16BE;
-SlowBuffer.prototype.writeInt32LE = Buffer.prototype.writeInt32LE;
-SlowBuffer.prototype.writeInt32BE = Buffer.prototype.writeInt32BE;
-SlowBuffer.prototype.writeFloatLE = Buffer.prototype.writeFloatLE;
-SlowBuffer.prototype.writeFloatBE = Buffer.prototype.writeFloatBE;
-SlowBuffer.prototype.writeDoubleLE = Buffer.prototype.writeDoubleLE;
-SlowBuffer.prototype.writeDoubleBE = Buffer.prototype.writeDoubleBE;