Lua 5.2 compatibility

[Kaixhin]

I get the following error when running luarocks install camera:

[100%] Building C object video4linux/CMakeFiles/v4l.dir/v4l.c.o
/tmp/luarocks_camera-1.1-0-8939/lua---camera/video4linux/v4l.c:644:30: error: array type has incomplete element type
 static const struct luaL_reg v4l [] = {
                              ^
make[2]: *** [video4linux/CMakeFiles/v4l.dir/v4l.c.o] Error 1

With a quick look it seems that this problem is due to Lua 5.2 missing luaL_reg.