merge -r1433:1434 from tags/release-1.6.0 to tags/release-1.6.1 (stable release required modifications: don't show version and generation time in footer, don't check the upgrade feed, don't die on sql errors).

git-svn-id: http://piwigo.org/svn/tags/release-1_6_1@1484 68402e56-0260-453c-a942-63ccdbb3a9ee