moved debug fn out to own module, added tests

lib/streams/BaseRollingFileStream.js

@@ -1,6 +1,7 @@
 "use strict";
 var fs = require('fs')
 , stream
+, debug = require('../debug')('BaseRollingFileStream')
 , util = require('util')
 , semver = require('semver');
 
@@ -10,13 +11,6 @@ if (semver.satisfies(process.version, '>=0.10.0')) {
   stream = require('readable-stream');
 }
 
-var debug;
-if (process.env.NODE_DEBUG && /\blog4js\b/.test(process.env.NODE_DEBUG)) {
-  debug = function(message) { console.error('LOG4JS: (BaseRollingFileStream) %s', message); };
-} else {
-  debug = function() { };
-}
-
 module.exports = BaseRollingFileStream;
 
 function BaseRollingFileStream(filename, options) {