Comment 6 for bug 801700

Attached you find an updated and extended patch for lp:mixxx #2915

Following changes are incuded:
* Tracks are now removed from the weak cache if they are deleted.
* The list of dirty tracks is removed from the trackDao because no one is using it.
* I have made the weak cache static, because I think there should be only one weak cache to share tracks between several instances of trackDao. (Although, today only the track collection is using the cache)
* If a caller gets the track from the weak cache, it is now added to the strong cache again.
* BaseTrackCache is updated from LibraryScanner per TrackPointer, smarter fix for bug #870544.
* Moved Tracks are also updated in the BaseTrackCache
* Tracks outside the library path are now verified too, fixes bug #239883.
* Up to 30% faster scanning a new library on my Netbook