Updater (command-line): add some code to ease debugging

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Updater (command-line): delete obsolete file versions in pristine mode

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Merge branch 'updater-pristine'

This fixes the bug that the Stable-Fiji job "forgot" to update the updater
itself: while the correct files were downloaded, the obsolete versions
were not removed -- and even favored by the package maker.