ES6: Added tests for each Proxy handler

This adds tests for the Proxy get, set, has, deleteProperty,
getOwnPropertyDescriptor, defineProperty, getPrototypeOf,
setPrototypeOf, isExtensible, preventExtensions, enumerate, ownKeys,
apply and construct handlers.
EJS support is inferred from the source.

Also fixes a few other results for old Firefox versions.

Sorry that this diff looks terrible, but if you run `git diff
--minimal`, it more accurately reflects the changes.
Added missing property names to the Reflect test
Added a Proxy.revocable test
Updated Proxy tests to multi-line comment strings

NOTE: this commit only updates data-es6.js.