More ORM model revisions in Item, Comment, and Task.
- fix ORM-referencing comments in Comment and Item.
- revise use of changes() in Item and Task.
- move common Item update/create code into a save() function.
- remove a couple redundant comments in Item.
- add comment_before_create and comment_before_update events.
Revise how Cache_Database::set_with_tags() saves the cache.  No net functional changes.
Revert some recent changes to index.php - make error reporting like Gallery 3.0.x.
Merge pull request #291 from shadlaws/more_fixes_20130415

More fixes 20130415