Missed an instance of _cacheitem
More logging scale back

Started printing the entire item when I fixed the olditems problem,
obviously that's too much.
Shrink the window in which index() holds tag and protect locks
Minor comment
Update lock header comment
Front-load set/delconfigs to hold on_config_change locks too
Fix exploding feed database

Wasn't properly detecting matching item ids with disk content, so the
new contents would balloon with duplicate items.
Spawn FetchThreads to populate items from disk only

This makes it spawn threads right before it begins to serve.

Before you'd have to wait for a network fetch to actually occur (or
timeout, either way).