quickchecking with whitelisting and opaque types

[shnewto]

The quickchecking crate, for property testing with fuzzed C headers doesn't exercise whitelisting or opaque types.

If those features were excercised, the tests might verify that if whitelisting is employed,
those types appear in the bindings and that anything flagged opaque isn't translated beyond "a blob of bytes".

Corresponds to extending #970