fix bug 1935

fix for bug 1935: https://processing-js.lighthouseapp.com/projects/41284-processingjs/tickets/1935-the-for-each-loop-over-arrays-doesnt-work-on-firefox-17#ticket-1935-2

Apparently FF now has an undocumented proto method called "iterator" for Array objects. That was the cause of the bug. No evidence of this iterator method was to be found on MDN: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Array