Lua 5.1 defines a "luaL_Reg" alias for deprecated "luaL_reg", but Lua >= 5.2 and LuaJIT do not. Replace by "luaL_Reg", and define a "luaL_reg" alias in case we build with old Lua 5.0. Signed-off-by: Manuel BACHMANN <tarnyko@tarnyko.net>