Our users could not decide whether they wanted extra whitespaces to be highlighted or not.  Some people love it, others find it too distracting, the more for legacy code.  This change provides a button, modeled on the collapse change button.  The choice is also saved in a cookie, so that each user can have her own preference.

This is different from Show/Hide Whitespace changes, and the 2 options cohabit well, I verified that after upgrading to 1.5 beta1.  (I had to change gt(0) to gt(1) in the javascript.  I would rather use a class name associated to the li tag, but I was concerned about a potential performance impact.)

I was also wondering if I should make it more dynamic, ala Show/Hide Whitespace changes, but I see it as a more static choice, depending on the code you're working on.

This has been in production in our local installation for over 6 weeks.