Added destroy method to Zlib object in zlib.js module

lib/zlib.js

@@ -427,6 +427,12 @@ Zlib.prototype.resume = function() {
   this._process();
 };
 
+Zlib.prototype.destroy = function() {
+  this.readable = false;
+  this.writable = false;
+  this._ended = true;
+};
+
 util.inherits(Deflate, Zlib);
 util.inherits(Inflate, Zlib);
 util.inherits(Gzip, Zlib);