Handle resend of multipart parts and reject resend if part size changed

[JustinKyleJames]

We need to handle a resend of a part when doing multipart uploads if the part size is unchanged.

I believe this should work if writing directly to iRODS and may work if writing to a local cache file.

• If writing directly to iRODS, this would just be a new open/seek/write so that should work fine.
• If writing to a part file, the part file would need to be truncated on open.

Even if both of these work, we would need to prove that they work and that will require writing a client using low level API's. (It's possible that this could be done with curl.)

We should also reject a resend if we detect the part size changed.