[ech] Loading time and flushing

[Watson Ladd]

Dear ECH enthusiasts,

I think the current API from Stephen Farrel for loading doesn't quite
work. If I understand correctly, the real time of loading is used to
determine when a key is timed out. In a fleet of servers a server may
restart during the validity time of a key, and thus would end up
retaining it longer. Thankfully this is not a big problem as servers
with additional keys can only decrypt more, unlike with shared ticket
keys where it could be more serious.

Sincerely,
Watson

-- 
Astra mortemque praestare gradatim