Lua >= Lua52

Housekeeping, mostly. Also switched the vim & macvim to Lua from Lua51
- Not doing so was an oversight on my part earlier. Also made some
changes to Luajit, because it installs empty directories named ‘Lua’ to
{share} and {lib} and those directories have the potential to screw
over other software hunting for libs. Luajit works fine without those
directories, so can be safely removed.