Allow uploading bogus new versions of unchanged files

There are projects advancing versions without any actual changes inside
the .jar file. We still need to support that use case, even if it
disagrees with the way ImageJ/Fiji themselves are developed.

This fixes https://github.com/imagej/imagej-updater/issues/9.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add regression test for the upload of bogus new versions

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>