Words to avoid cross browser compatible

https://www.pivotaltracker.com/story/show/68621758

on IE8 and below we will disable highlighting
but retain the alert box on the right.

![screen shot 2014-04-03 at 11 20 57 am](https://cloud.githubusercontent.com/assets/230074/2602278/f0308358-bb1c-11e3-94b8-c2ff4d4357a4.png)

highlighting breaks on these browsers because
the plugin relies on copying text out of a text area
working properly. this is not possible on IE 8 and
below because on those browsers newlines and
white-spaces are lost when text is copied out of
a text area.

whereas, on all other browsers we will enable
alerting as well as highlighting. the count here
reflects the instances of words highlighted.

![screen shot 2014-04-03 at 11 25 38 am](https://cloud.githubusercontent.com/assets/230074/2602279/f0320520-bb1c-11e3-8870-43f8be703f42.png)

i'm open to suggestions about how we can avoid
the difference in counts across these 2 implementations.

@edds - would like to get your inputs
@benilovj - you're new to this feature, so it'll be good to know your thoughts as well.

History: https://github.com/alphagov/whitehall/pull/1359