const-oid: provide shortest_by_oid lookups

[baloo]

see #1121

[baloo]

Provided a couple fixups to make the dependency tree happy that looks like it works:

Running tests/name.rs (target/debug/deps/name-2a144d2ccb8c9eae)
running 3 tests
test decode_rdn ... ok
test decode_name ... ok
test rdns_serde ... ok
test result: ok. 3 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

That would require a const-oid 0.9.3 backport if we want to release that without too much hassle.

[tarcieri]

@baloo I had something a little bit different in mind.

I was thinking of adding a method which returns an Iterator<Item = &'a str>, e.g. struct Names<'a>, which iterates over all of the names for a given OID. I'm not sure of a good name for it given the current naming scheme, but otherwise something like Database::find_names_for_oid.

If you have that iterator you can implement shortest_by_oid as a private function in x509-cert, although we could add it to const-oid if there are use cases outside of X.509.

[tarcieri]

@baloo can you split out the const-oid changes so we can merge them separately? I can take care of the backport

[baloo]

Yes, I'll try to do that tonight. And also update the comment !!

[baloo]

Closed in favor of #1129 and #1130