[server/session] add missing rollback when freeing a db connection When we let go of a cnxset and give it back to the pool, we need to make sure it's not in the middle of a transaction. We got bitten by a migration where the connection used by admin's repo.connect was not rolled back before attempting the migration, causing a deadlock because it had a lock on a table. This could potentially also be an issue for e.g. hooks or looping tasks that didn't explicitly rollback before calling free_cnxset or moving out of a ensure_cnx_set block.

bgcolor = '#000000'
stylesheets = ['%s/cubicweb.css' % datadir_url]
logo = '%s/logo.png' % datadir_url
lazy = lazystr('%(bgcolor)s')