Fix LuaJIT exception wrapper

This reverts the LuaJIT exception wrapper to the recommended version shown at:
http://luajit.org/ext_c_api.html#mode_wrapcfunc

The current exception wrapper fails to handle C++ exceptions thrown inside C++ code called from Lua. This is why the error message in #1556 is just "C++ exception" and nothing more specific.

To test this fix, apply #1579 and run the chat command "/exceptiontest immediate exception" in the minimal game.