WIP es7 compliant contains

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

ff 34:

```
contains nan-branch x 6,651,589 ops/sec ±6.09% (53 runs sampled)
contains naive x 4,524,408 ops/sec ±4.50% (53 runs sampled)
contains y=y x 4,524,408 ops/sec ±4.50% (53 runs sampled)
```

safari 8
```
contains nan-branch x 3,239,116 ops/sec ±4.70% (51 runs sampled)
contains naive x 2,425,872 ops/sec ±3.90% (51 runs sampled)
contains y=y x 3,417,143 ops/sec ±3.82% (55 runs sampled)
```

chrome 40 (64bit)

```
contains branch x 3,952,907 ops/sec ±3.84% (54 runs sampled)
contains naive x 1,796,188 ops/sec ±3.26% (52 runs sampled)
contains y=y x 3,587,872 ops/sec ±3.10% (55 runs sampled)
````