Improve implementation of LS.getclass and LS.classname, make it more consistent.

luprex/cpp/core/source.cpp

@@ -21,7 +21,7 @@ LuaDefine(makeclass, "classname", "create a class if it doesn't already exist")
     LuaArg classname;
     LuaRet classtab;
     LuaDefStack LS(L, classname, classtab);
-    if (!LS.validclassname(classname)) {
+    if (!sv::is_lua_classname(LS.ckstring(classname))) {
         luaL_error(L, "invalid class name: %s", LS.ckstring(classname).c_str());
     };
     LS.makeclass(classtab, classname);