upgrade_feed.php are now made by dedicated function
get_available_upgrade_ids.
bug fixed: after an installation, you had to play all available upgrades,
which was wrong. install.php inserts informations related to all available
upgrades at installation time. Thus avoiding automatic upgrades.
git-svn-id: http://piwigo.org/svn/trunk@1027 68402e56-0260-453c-a942-63ccdbb3a9ee