[development] Filter cache

[Gerhard Killesreiter]

Those of you who actually read my recent treatise about my "split cache 
table" patch might recall that I mentioned that drupal.org had a 
modification to stock Drupal, namely that it would cache filter items 
only for 4 instead of 24 hours.

When we did this we had on average have about 70000 cached filter item.

Now, we are actually caching the items for the full 24 hour period. One 
could be afraid that the number of cached items would grow a lot. It 
indeed did grow, but not by a factor of 6 but only by a factor of about 2.

I am inclined to further increase the cache period and try to see where 
the number of cached items goes and if it helps drupal.org's performance.

One would hope that the filter table would become somewhat stable and 
could maybe reside fully in memory on the sql server. However, there is 
of course a memory limit to this, the cache_filter table already has 
about 120 MB.

Cheers,
	Gerhard