Mark the isH2ModeMySQL, isMySQL, isFirebird, isMSSQLServer fields as private because they are not accessed outside this class.
Remove the storedUpperCaseIdentifiers field because it is not read from anywhere.

Converted it to log the exception at debug level, since that is what the comment indicates.

A persistent multi-version map: explicit map creation; change map factory to become just a factory for data types again

Also remove an unnecesssary copy of the closeSilently() method

Serialization is now pluggable using the system property "h2.javaObjectSerializer". Thanks to Sergi Vladykin for the patch!

A persistent multi-version map: open the file in exclusive or shared mode; allow to read and update the file header.

Fix ConcurrentModificationException when creating tables and executing SHOW TABLES in parallel. Reported by vvoytovych@llnw.com.