Addresses placeholder text remaining visible on focus in Chrome

The placeholder attribute in Chrome does not work to spec. This makes the text transparent on focus to work like Firefox, Safari, and the spec. Credit goes to @chadbaudoin for bringing this up in his pull request https://github.com/necolas/normalize.css/pull/86 and this Chrome bug is further documented at http://code.google.com/p/chromium/issues/detail?id=106714  and my own test is at https://tinker.io/be2f2/1