[fix] do proper streams2 detection so we dont cause possible slowdown…

…s when writing to file fixes #296

lib/winston/transports/file.js

@@ -13,6 +13,7 @@ var events = require('events'),
     colors = require('colors'),
     common = require('../common'),
     Transport = require('./transport').Transport,
+    isWritable = require('isStream').isWritable,
     Stream = require('stream').Stream;
 
 //
@@ -53,7 +54,7 @@ var File = exports.File = function (options) {
   else if (options.stream) {
     throwIf('stream', 'filename', 'maxsize');
     this._stream = options.stream;
-
+    this._isStreams2 = isWritable(this._stream);
     //
     // We need to listen for drain events when
     // write() returns false. This can make node
@@ -168,7 +169,7 @@ File.prototype.log = function (level, msg, meta, callback) {
 File.prototype._write = function(data, callback) {
   if (this._isStreams2) {
     this._stream.write(data);
-    return process.nextTick(function () {
+    return callback && process.nextTick(function () {
       callback(null, true);
     });
   }
@@ -183,7 +184,9 @@ File.prototype._write = function(data, callback) {
       callback(null, true);
     });
   }
-  callback(null, true);
+  process.nextTick(function () {
+    callback(null, true);
+  });
 };
 
 //
@@ -438,7 +441,7 @@ File.prototype._createStream = function () {
       self._size = size;
       self.filename = target;
       self._stream = fs.createWriteStream(fullname, self.options);
-
+      self._isStreams2 = isWritable(self._stream);
       //
       // We need to listen for drain events when
       // write() returns false. This can make node