Keyring collection support project review

[Greg Hudson]

We plan to augment the existing KEYRING ccache type for 1.12 to support
credential cache collections and to support the new persistent key type.
The project page is here:

    http://k5wiki.kerberos.org/wiki/Projects/Keyring_collection_cache

I am currently working on integrating Simo's implementation with some
changes.  Before it is merged, the planned implementation will be here:

    https://github.com/greghudson/krb5/commits/keyring

Comments are appreciated, although the timeline for this work is
unfortunately short.