sync-with-imageJ: do not trust <latest>

It seems that the <latest> tag does not get updated properly. At
least it seems that with -DupdateReleaseInfo=true, even Maven 2
deploys things in such a way that <release> gets updated. So trust
that instead.

Noticed by Curtis Rueden.

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