November ES6 spec changes

This adds/removes/changes the following tests:

* RegExp.prototype methods
* Symbol.species
* String.prototype.includes
* WeakMap/WeakSet.prototype.clear
* Array.isArray on proxies
* JSON.stringify on proxies
Merge pull request #338 from webbedspace/november

November ES6 spec changes
Removed ES6 compiler test pages from version tracking.

Since these are not public-facing, take a good while to re-compile, and make more complicated diffs, there's little reason to keep them tracked.