1. TD < 2 in a row
2. TD <= 50% of total cells
3. Not all table rows can be THEAD rows

source maps are invalid for our dispatched sources and may even cause
problems. this makes sure any sourcemap declarations are stripped from
the output

This adds a warning in the case that the default action is not null but
also not callable which can happen when the supplied method is not
public.

Caching had been completely broken (disabled) for caches with events
because the default event handler (cache::_useCache()) was protected and
thus couldn't be executed by the event handler. This was broken in
c59b3e00

1. renderer validity checks were too stringent for plugins, format
   should only need to be checked when mode is 'xhtml'
2. E_USER_WARNING message should now be obsolete, its previous use
   was to generate a warning when 'xhtml' rendering failed. PR#571
   insures 'xhtml' rendering always succeeds.

Run jpeg meta tags through cleanText for a conversion to UTF-8
from latin-1 if possible.  MediaManager already uses this
conversion.  Addresses a side issue of FS#1988

The existing function was difficult to follow.  It worked when
adding a new tuple, but not in the most sensible manner.