CMakeLists.txt:  Lua5.2 support.

Because the current Debian unstable is using

  * Luabind which is depending on Lua5.2

  * LuaJIT which has a Lua5.1 API

the code were using the Lua5.1 header files but were linked against
Lua5.2 library.

Now both are using Lua5.2 (libluajit-5.1-dev must not be installed
during CMAKE !), which seems to work for the OSRM-Extractor.