Try versioned "lua" names before the unversioned one.
Should improve on behavior mentioned at
http://stackoverflow.com/questions/20321560/how-do-install-libraries-for-both-lua5-2-and-5-1-using-luarocks/20359102?noredirect=1#comment30696438_20359102
Merge branch 'master' of github.com:keplerproject/luarocks