error message only highlights on mouseover

[shriram]

r = reactor:
  init: init-state,
  update: update
end

(assume update is defined). The error is the reactor handler named update, which should be called on-tick. The error reads

but there is no associated highlighting. However, when you hover over the "definitions…" line at the bottom of the error, the corresponding code does highlight…for some reason it doesn't unless you do.

[blerner]

I actually literally fixed this last night, since it was annoying me. If you try this on pyret-horizon right now, you'll get

It's debatable whether highlighting "Well-formedness" is the best place to put the highlighting, but it's better than the message above. @jswrenn if you decide to revise these messages further: I've updated the signature for wf-err so that instead of taking a mere String as argument, it takes a List<ErrorDisplay> so that you can have richer output here.