Added initial vardiff. Needs testing...

lib/pool.js

@@ -1,7 +1,7 @@
 var events = require('events');
 var async = require('async');
 
-var varDiff = require('./varDifff.js');
+var varDiff = require('./varDiff.js');
 var daemon = require('./daemon.js');
 var stratum = require('./stratum.js');
 var jobManager = require('./jobManager.js');