Fixed errors thrown by `supports`, `getrandomvalues` and `flash` detects:
- `supports` incorrectly assumed that `window.CSSRule` would always exist
- `getrandomvalues` hit an odd bug in Safari, which exposes `window.crypto` but it’s undefined
- `flash` was trying to attach an `<embed>` element to the `<html>` element, which isn’t valid – so switched to using (a potentially fake) `<body>` instead
Merge pull request #1284 from stucox/1284-browser-errors

Test errors in some browsers