#411 precache_gse can be smarter

[Jamie McCarthy]

With the demise of the sectioncollapse var, I commented out that
part of the precache_gse task, so now it's only loading the plain-
vanilla, totally stock homepage request into the query cache.

What it should do instead is check a var to see what the top n
settings for story_{always,never}_* are. The n should probably be
2, maybe 3, and it should probably not include any settings that
are less common than 5% of the userbase. Maybe the var could be
a list of data to feed into gSE() in a space-separate list of strings
formatted like

tid=1,3,5,7,9;tid_x=2,10;uid_x=321

Once a day, in the daily.pl task somewhere, we should do a big old
GROUP BY select on the users whose users_info.lastaccess's are
within the last 30 days or something.

[Jamie McCarthy]

Logged In: YES
user_id=3889

This is still a good idea, but it'd be a feature, not a bug.