Mozilla's original implementation of this failed a couple of tests, but this seems to solve all the problems. Basically, the caret-color wasn't able to be set differently based on whether a link was visited, and the auto value implementation was incomplete. The only test we fail now is the one where you have grey text on a grey background and the caret is supposed to be visible, but I think that may have been removed from the spec. Even if it wasn't, no other browser supports it anyway.
Since these are just interpreted comments, there's 0 impact on actual code.
This removes all lines that match /* vim: set(.*)tw=80: */ with S&R -- there are
a few others scattered around which will be removed manually in a second part.
This updates our behavior for computed DOM styling to no longer return
null on elements that have no display, but return a 0-length (empty)
style instead and don't throw. For this we stop looking at having a
presentation for the style and just look at the document instead.
This resolves#1219
