Two bugs, with fixes. Found by turning on WP_DEBUG in wp-config.php, and some debugging lines in wp-admin/includes/upgrade.php.
1. In relevanssi_update_log() in 'lib/common.php', a wpdb error due to undefined $relevanssi_variables['relevanssi_log_table'].
2. In relevanssi_create_database_tables() in 'lib/init.php, a wpdb error due to missing linefeeds passed to dbDelta(), again with the table relevanssi_log_table. The dbDelta() function is very particular about syntax and it's not well-documented. The errors don't really appear unless you uncomment some echo lines in upgrade.php (and maybe add more echo lines and exits!).
Both errors can be fixed in init.php. Here is a patched version: