Fixing something silly

This part seems highly untested and raw... in pcall you have to call a function, not a string..
Fixing many issues and breaking compatibility with LuaTeX < 0.45 (TeXLive 2009)

There were several bugs in there (especially when the file asked ends by '.lua'), but seems ok now. Most of the old code has been removed, as the documentation said the next version would be only compatible with LuaTeX >= 0.45.
Fixing many issues and breaking compatibility with LuaTeX < 0.45 (TeXLive 2009)