Slide HTML view
Fix unicode handling again.

I was wrong, convertTo() input and output is binary, with a encoding
parameter that indicates input. However, plone.app.textfield decodes
by this same parameter, so the output has to be binary encoded by the
same encoding as the input.
I need to do this, but comment is getting in way
Remove leftover code, add a error instead
Add pre and postamble so TtM understands more stuff