FTAM — Cannot transfer files if Files have same associated_session

This issue concerns the operation:
FileTransferSession::transfer(in File src, in File dest)

and the associated operations append and insert.

As described in section 4.5.2, in the transfer implementation, the
FileTransferSession must first determine whether it is associated with
the src or dest File in order to set up an active or passive
connection.

If it is the source, it sets up an active connection and then calls
`transfer' again on the destination File's associated_session.
Unfortunately, when both the src and dest files have the same_session,
a FileTransferSession will always consider itself the source and
unwanted recursion will result.

The spec could say its forbidden to transfer files associated with the
same FileTransferSession but this is extreme.

It is also problematic to guarantee an implementation can detect this
situation, as the FileTransferSession interface has no identity
operations and a false return from is_equivalent is inconclusive. (The
is_equivalent problem is also raised in Issue 4183).

As with issue 4183, this issue could be resolved by not using the same
transfer method to both initiate sending and receiving of data.

The resolution for issues 4177, and 4209 resolves this issue.