Make binding/lua/Makefile more distributor friendly
Make binding/lua/Makefile more distributor friendly

This adds a USE_SYSTEM_LUA variable, which (when set to non-"no")
picks up the system lua without fetching and building any dependencies
and allows installation into the appropriate directory.

This also respects systems CFLAGS if set.

tarruda/libmpack,libmpack/libmpack,lourkeur/libmpack