while we wait for a sane "prefixing", use a much more efficient way to find errors

This comes from an unfortunate choice of naming conventions and the fact that 
manage errors gets called even on the full document on page load.
I had a table full of .error-"classed" elements and it took nearly 30 seconds for that
snippet to hide and fade them in. We should definitevely prefix every css class with
something that won't clash with everything else.
Merge pull request #524 from niphlod/js/speed

Waiting for a sane "prefixing", a much more efficient way to find errors