WIP es7 compliant contains

- [x] es7 polyfil for contains
- [ ] get review on the poly

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- [ ] make enumerable stuff work correctly (ideally without lots of duplication)
- [ ] transition SHIM_ES5 to SHIM_ESNEXT

It's the `arguments` object use that's the stinker (a reason Firefox used default params in their implementation). See http://jsperf.com/contains-vs-index-of/7#chart=bar.