Fix Updater: make initial comment nicer

This is intended to be the first step towards a script that can be
run in vanilla ImageJ to turn it into a Fiji installation.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix Updater: make sure that ij.dir is set

This is intended to be the second step towards a script that can be
run in vanilla ImageJ to turn it into a Fiji installation.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Fix Updater: make sure that the Fiji update site is active

This is the final step: running Fix_Updater.js in a vanilla ImageJ
will install all of ImageJ2 and Fiji into the same location.

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