Regarding Resetable and PositionedStream (PS), the former is more tightly bound to store.
For instance, initStream handles locking, which is probably not required for data streams outside of store. I don't see any immediate need to add the three methods resetStream, initStream and closeStream to LOBInputStream.
I'm opting for committing what I have now, and look at combining the interfaces later if it turns out that is the best thing to do.
I attached revision 1b, which adds two debug blocks (checking for a negative requested position), removed the throws clause for EOFException and fixed some errors in the JavaDoc.
After rerunning the tests, I intend to commit patch 1b.