Fix index creation 3

[dartcafe]

• The check for existing index names has to be case insensitive for PostgreSQL
  changed strpos() to stripos()
• DBALException was catched, but Exception was thrown
  Changed catch from ...\DBAL\Exception to \Exception
• Primary keys could have been dropped in hard fallback
  Secure PKs when dropping unique indices
  Added a repair step to restore PK on accidentially drop