improving installer : now the database Version is compared to the Koha version (defin...

improving installer : now the database Version is compared to the Koha version (defined by <kohaversion>XXX</kohaversion> in koha.xml file. If the Version systempref does not exist or is lower than kohaversion, you're redirected to installer. If there is no Version, you're redirected to the 1st step of the installer (full install). If Version < kohaversion, you're redirected to step 3 (updatedatabase). check that you have <kohaversion> in you koha.xml, otherwise, you'l loop forever to the installer...