#3863 / DB Update Fails: Expected no record, got 2 rows: SHOW TABLE STATUS WHERE Name='Form'

Introduce new config var 'DB_UPDATE' in config.qfq.ini. Update the handling, if there exist table 'form' and 'Form'.
Manual.rst:  document the new config option DB_UPDATE.
Database.php: Typo fixed.
DatabaseUpdate.php: Iterate over all found 'Form' tables, take the newest version number. Respect config option DB_UPDATE. Fixed a problem: if in the PHP DB updates a newer DB Version is configured than the PHP source itself is, such updates are now not played anymore.
Config.php, QuickFormQuery.php, config.example.ini: handle config setting DB_UPDATE.