Immortal Lifetime logic is… odd

[battis]

Right now, you can only look up cached values that have IMMORTAL_LIFETIME if the SimpleCache object has had its lifetime set explicitly to IMMORTAL_LIFETIME. This is dumb and stupid. Setting the cache object lifetime should affect the default lifetime of newly cached data, but the the expiration dates of currently cached data should be all that limits getCache() responses -- and data with perfectly good immortal lifetimes should be found!

N.B. that it is possible that changing this logic will necessitate dramatic version number increases. Think carefully!