Cleanup data.splits

[SLaks]

I handled the model cleanup event to empty the splits cache.

This fixes #72.

[lefnire]

Holy crap! I'm gonna test this on Habit today, this may be the holy grail!

[SLaks]

This alone will not solve server memory leaks.

Leaking models will consume far more memory than only data.splits;you should really try to remove the leak entirely.

Also, this will only do anything when those models emit a cleanup event, which by default only happens every 128 event handler registrations.

[lefnire]

I see. I thought the leaky model was only a result of data.splits build up, I got ahead of myself :)

[SLaks]

data.splits is a big (in memory consumption) part of a model, but the rest of the model (the actual data, the query descriptors, etc) is even bigger.

[SLaks]

This was removed by 920784f