MVStore: unique indexes that were created later on did not work correctly if there were over 5000 rows in the table.

For Windows, database URLs of the form "jdbc:h2:/test" where considered relative and did not work unless the system property "h2.implicitRelativePath" was used.

In server mode, appending ";autocommit=false" to the database URL was working, but the return value of Connection.getAutoCommit() was wrong.