Restore original meaning of disguised attribute.

Certain types like GIConv and GdkAtom are pointers internally but don't look like pointers when referenced. They have the form.

typedef struct _X *X;

Parse these as structures/records but mark them in the gir with a 'disguised' attribute so that we know that they need special handling.

Additionally, stop relaying on disguised attribute when deciding whether to render a page. Check number of fields instead, so as to avoid introducing large regression in the docs.

Fixes #101 (closed).