fixes #40: remove "use strict" from files where IE gets confused

Remove "use strict" from files that have assignments of the form `arguments[x] = y`, this pattern confuses IE 11.

Another option would be to copy the array so IE is more happy. I'm not sure which solution is more performant/better. Do any engines optimize strict mode? If they do, I'd hate to have events.js lose that. OTOH, the extra copy seemes unfortunate. And other polyfill & polymer code don't generally use strict mode. Though I personally think it's pretty neat.

@arv do you have any thoughts?