[krbdev.mit.edu #8187] keyring ccache forgets default principal upon expiration

[Greg Hudson via RT]

When a KEYRING ccache expires, not only do the creds go away, but the 
default principal becomes inaccessible as well.  This can be 
inconvenient when refreshing the credentials in the ccache.

This was reported verbally to me by Viktor Dukhovni; I haven't 
personally verified it.  I also don't know offhand how difficult it 
would be to change.