The Lua Class is not a meta table now. It is a normal table, has a key named ".isclass", and a meta table has been set to it.
To judge a Lua Class's type, must use it's meta table.
All the origin keys (in c/c++) were stored in Lua Class's meta table (and it's "parents's" meta table) .
If a origin key was overrided in Lua, it was backup in a table named ".backup". This backup table is a key of the meta table.
ONLY a origin key was overrided, you can use "tolua.getbackup(class or object, key_name)" to return it, otherwise, the function return nil.
Merge pull request #365 from SunLightJuly/get_override_c_function

The Lua Class is not a meta table now. It is a normal table, has a key n...