Verify that the Sauce readyFile has changed

The readyFile watcher may emit multiple events. Dig Dug should only pay
attention to the first one in which the readyFile was modified.

SauceLabsTunnel.js

@@ -424,7 +424,12 @@ SauceLabsTunnel.prototype = util.mixin(Object.create(_super), /** @lends module:
 
 		// Polling API is used because we are only watching for one file, so efficiency is not a big deal, and the
 		// `fs.watch` API has extra restrictions which are best avoided
-		fs.watchFile(readyFile, { persistent: false, interval: 1007 }, function () {
+		fs.watchFile(readyFile, { persistent: false, interval: 1007 }, function (current, previous) {
+			if (Number(current.mtime) === Number(previous.mtime)) {
+				// readyFile hasn't been modified, so ignore the event
+				return;
+			}
+
 			fs.unwatchFile(readyFile);
 
 			// We have to watch for errors until the tunnel has started successfully at which point we only want to