Use "unsigned int" rather than "size_t" in lua bindings.
Use "unsigned int" rather than "size_t" in lua bindings.

Since tolua++ doesn't understand size_t and treats it as userdata.
There will be loss of precision on 64 bit systems, but this only comes into
play if there are more than 4,294,967,296 child windows, so I think it's
something we can live with.
This fixes issue #1000

arkana-fts/cegui,RealityFactory/CEGUI,cbeck88/cegui-mirror,RealityFactory/CEGUI,arkana-fts/cegui,cbeck88/cegui-mirror,arkana-fts/cegui,RealityFactory/CEGUI,cbeck88/cegui-mirror,cbeck88/cegui-mirror,arkana-fts/cegui,arkana-fts/cegui,cbeck88/cegui-mirror,RealityFactory/CEGUI,RealityFactory/CEGUI