Only consider the most recent entry in the user cache
Only consider the most recent entry in the user cache

This gracefully handles the situation in which a user
increases the expiration timeout with an already-populated
cache as well as the problem with inconsistent information
in the cache (as the most recent entry now always wins).

Working on #670

jh23453/privacyidea,wheldom01/privacyidea,jh23453/privacyidea,wheldom01/privacyidea,jh23453/privacyidea,wheldom01/privacyidea,wheldom01/privacyidea,privacyidea/privacyidea,jh23453/privacyidea,wheldom01/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,jh23453/privacyidea,wheldom01/privacyidea,jh23453/privacyidea