2.4 API additions

[jeremy-visionaid]

Adds the following methods:

• CompoundFile.Dispose (as public)
• ContainsStream
• ContainsStorage
• TryDelete

While adding them, I found some problems with the existing implementation that I have fixed since it made sense to do so at the same time:

• RBTreeEnumerator performed multiple enumeration on a Queue via LINQ, but RBTree did not support LINQ (IEnumerable)
• Directory resets invloved multiple redundant casts and lookups