Bug 20254: Do not ingest files with duplicate filenames

Bug 20254: Do not ingest files with duplicate filenames

If the supplier delivers the same file twice we are
unable to rename it on the second occurence causing us to download
and process it infinitely.

Check that downloaded filenames are unique against those
on file and reject processing if a duplicate.

This patch delays this check to the ingest stage so that the
same code is processed irrespective of transport

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>