[Context] update before building & fixing some issues

Hello, Just in case - please update the building script before executing it since location of metapost binary has changed. Taco - we had to re-add dvitomp binary a while ago for some reason I forgot. Is that file still needed and why (not)? One more thing: I'll try to fix a few issues in the minimals next week (the most important one would be sorting out which luatex binary to use and to enable choosing "experimental" version of luatex, but there are definitely more issues). I need to prepare a list, but I'll start concentrating on the issue next week. You may put your ideas on the wiki or to the tracker or just reply here. Mojca