Let copy-jars warn about obsolete files, possibly delete

If the configuration setting deleteOtherVersions is set to false
(the default value), we warn about files in the target directory
which disagree with the artifact to-be-copied only in the version.

If deleteOtherVersions == true, we delete them.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Touch up a JavaDoc

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add an integration test for deleteOtherVersions

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add an integration test for deleteOtherVersions == false

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Heed deleteOtherVersions even if the target was up-to-date

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