[Context] some changes in binary compilation

Hello, I'm going to change some aspects of binary compilation in order to enable storing multiple versions of luatex. I have to watch out to make the changes more or less simultaneous. There has been a recent change/patch in pdftex, but assuming that Taco is not going to release the next version of LuaTeX or metapost in the next few days ... I just wanted to warn you that compiling the binaries until my next notice might fail if you start compiling in the wrong moment during transition. After that I will ask you to update build-binaries script to account for the changes. Mojca