fixed fail on processing headers with substring 'type' in their names

Hi @scopatz. We are using xdress to create python bindings for sdk written in 'c' and faced with issue when xdress fails on processing 'c' headers with 'type' in their names (e.g. we have types.h in our sdk). In such case module description is considered as variable description. I added additional verification for it, but not sure that it's right solution.