[THREDDS #GYQ-484919]: cache configuration

Hi Fan,

Great, I'm glad it's working! This was a weird corner case. FileCache looks at 
a dataset's last-modified time in order to detect if an entry is stale and 
needs to be refreshed. Checking that is easy if the dataset is local; the OS 
can tell you. But for OPeNDAP (and probably other remote formats), that info 
isn't readily accessible. So we just assume those remote datasets never change. 
And so the cache can grow stale.

Cheers,
Christian

Ticket Details
===================
Ticket ID: GYQ-484919
Department: Support THREDDS
Priority: High
Status: Closed
===================
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