rustdoc: broken links to `rand` from `std`

[durka]

If you go to a place in the libstd docs that references the rand crate, such as here, all the links (1, 2, 3) are broken. Looks like they need an extra "/rand/" in the URL. The same problem occurs in the nightly docs (not sure what the correct URL is for those, though).

Since these links to trait impls are auto-generated by rustdoc, I'm assuming this is a bug in rustdoc, not just a typo in the documentation. Or it has something to do with the rand code existing in libstd but also librand.

[steveklabnik]

Or it has something to do with the rand code existing in libstd but also librand.

I believe this is the cause. @alexcrichton any ideas?

[alexcrichton]

Ah yes this is just a private trait in the distribution, so it just needs to be marked #[doc(hidden)].