WIP: fix(client): hide the homegrown show/hide password button for IE8 and browsers that have their own `reveal` mechanism.

fixes #1114
Since we're now "tainting" 3rd party code with our own code, I can tweak the [JSHint paths](https://github.com/mozilla/fxa-content-server/blob/master/grunttasks/jshint.js#L24) to exclude the /vendors/ folder but then _**include**_ just the _app/scripts/vendor/env-test.js_ file if you want.