add SDL as an dependency

let animation objects delete themselves after they are not being used anymore PS: I don't like that we create new animation objects every single time before a page transition is done, I'm sure that can be done in a nicer way. But at least we're not keeping those non-reused objects around forever now...

revert tremor back to a version before koda broke it ;p

more like here

merge Medo's GSoC work

Workaround for visual bug. issue #442