Add 'use strict', fix global leak

resemble.js

@@ -6,6 +6,7 @@ URL: https://github.com/Huddle/Resemble.js
 */
 
 (function(_this){
+	'use strict';
 
 	_this['resemble'] = function( fileData ){
 
@@ -449,7 +450,8 @@ URL: https://github.com/Huddle/Resemble.js
 
 		function getCompareApi(param){
 
-			var hasMethod = typeof param === 'function';
+			var secondFileData,
+				hasMethod = typeof param === 'function';
 
 			if( !hasMethod ){
 				// assume it's file data