Rethink Diff Database Storage

[tomrittervg]

We store the changed texts of diffs, for commit.getChangedTexts. I did this because those objects are used for the fulltext search, and thus should be fast.

But the database does not store the diff objects from commit.getDiffsArray. Those diff objects are only used for the internal diff display (which isn't very good anyway) - but when you hit one of those internal diff displays, it does take a lot of disk i/o.

Maybe I could store an intermediate representation that could be used by both of these?