[dev-context] latest beta (tests needed)

Hi, Hans, you are almost there, afaik. A few notes still: * The new bibliography module. It would be more comfortable if the t-bib was in tex/context/bib like before. It is now in tex/context/third, like in my zipfile, but that is searched later, so I now had to delete the old one manually. And if you want to promote it to core status anyway ... * A small fix to verbatim (color) * The improved version of math substacks. (looks fine) * The xtag-mml patch. * The \dodoregister patch. Duncan, can you check if these last two items are ok now? Taco