Handling iteration over inherited properties before own properties. Fixes #12199

I added an `iteratesOwnLast` property to `jQuery.support` to check for browsers that iterate over inherited properties before own properties, which only seems to be IE < 9. I used the same [technique that lowdash uses](https://github.com/bestiejs/lodash/blob/7520066fc916e205ef84cb97fbfe630d7c154158/lodash.js#L134-144).

In `jQuery.isPlainObject`, I also followed [the technique in lowdash](https://github.com/bestiejs/lodash/blob/7520066fc916e205ef84cb97fbfe630d7c154158/lodash.js#L741-L747) to handle `iteratesOwnLast` browsers.

Let me know how it looks.