[dev] Horde_Cache index

[Duck]

As manly the cache demons don't support listing entries by criteria or even 
just listing keys (ex. Memcacehd). I would like to add an cache index to the 
Horde_Cache. This will allow us to delete  group of entries. For example in 
Agora if we cache the rendered threads on a new submission we must delete all 
the thread sub-pages and different sort directions etc. Or perform a garbage 
collection per each application. Of course the indexing would be a option, 
loaded only when need.

This mean store the cache index in DB. Accessed only when a new entry is 
created or deleted. Or has anybody a better option?

Duck