Media is reindexed each time backend is started

[Joshua Scotton]

Media is reindexed each time the backend is started.

The desired behaviour should be the backend just checking for changes to the existing index of movies, music etc.

[Paul Hummer (rockstar)]

I think it's important that I document on this bug where we are with this process. The ImageCache work is completed on the backend, and just needs a bit more forward porting on the frontend. However, I now have more than a deep understanding of why exactly it re-indexes everything. There are a few reasons for this:

1) When calling update on the old data model, it deleted everything and reindexed everything.
2) On each startup, MediaCacheManager.rebuild*Cache is called which deletes and re-creates this.

The fix is actually a lot more trivial than I was expecting it to be. I plan on fixing this after all the cache classes have been ported to the new data model.

As a side note, tracking this down was nice, because it clearly laid out an upgrade path for new iterations of the data model. We can harness this same concept to trigger when a table needs to be rebuilt with a new structure. Blessing in disguise (and, I'm starting to think, was the original idea behind this constant re-indexing).

[Matt Layman (mblayman)]

I'm not marking this as Fix Released because the code is only on the 0.3 branch and not the trunk. I think we can release it after we merge 0.3 fixes onto trunk.