moved debug fn out to own module, added tests

lib/streams/RollingFileStream.js

@@ -1,17 +1,11 @@
 "use strict";
 var BaseRollingFileStream = require('./BaseRollingFileStream')
+, debug = require('../debug')('RollingFileStream')
 , util = require('util')
 , path = require('path')
 , fs = require('fs')
 , async = require('async');
 
-var debug;
-if (process.env.NODE_DEBUG && /\blog4js\b/.test(process.env.NODE_DEBUG)) {
-  debug = function(message) { console.error('LOG4JS: (RollingFileStream) %s', message); };
-} else {
-  debug = function() { };
-}
-
 module.exports = RollingFileStream;
 
 function RollingFileStream (filename, size, backups, options) {