Use for loop instead of for/in loop to protect sanctity of Array.prototype....

Use for loop instead of for/in loop to protect sanctity of Array.prototype. Fixes #7817. Test case for this commit is shared with the fix for #6355, https://github.com/jquery/jquery/pull/140 .

src/xhr.js

@@ -87,7 +87,7 @@ jQuery.xhr = function( _native ) {
 		}
 		
 		// Apply option prefilters
-		for (i in prefilters) {
+		for ( i = 0; i < prefilters.length; i++ ) {
 			prefilters[i](s);
 		}