ES6 Math functionality checks

Some Math functions' tests have been upgraded from mere existence to basic functionality. These are not supposed to test much beyond a basic result or two, to at least determine that they quack like the intended
mathematical function.

This may seem spurious, but note that Konqueror 4.13's `acosh` is actually implemented to behave like `asinh` due to that bug I mentioned [some months back.](https://github.com/kangax/compat-table/pull/183#issuecomment-51328736)