Lua works!

Lua works!
I don't even have to write a context mechanism. Lua vm's fine with
having swapcontextes changing the world around it. It's also fine with
threads doing so, as long as they dont do it at the exact same time
(but we're just fine in SimGrid).

Some more cleanups are needed, I guess.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/simgrid/simgrid/trunk@7340 48e7efb5-ca39-0410-a469-dd3cf9ba447f