sqlite db task queue

[amv]

Should eliminate SQLite db access concurrency within single process.

Also contains small fixes to make lint happy.

This is completely untested code. Can you please test this before making a release and pushing this to production? :) :P

[amv]

I remembered that we had actual integration tests, so I ran them! Found one bug, but after fixing it, the tests pass like they do in the sqlite branch.

It would be nice to have you run your "load testing" scripts for this version also if you still have them handy.

[amv]

Fixed all sqlite integration tests and made the lock global to the whole process, not just the db object.

load testing would still be nice, but i think this is starting to be merge ready..