Fix bug which could generate a NegativeArraySizeException when performing large (>40M) row union operations

Server mode: the transfer buffer size has been changed from 16 KB to 64 KB, after it was found that this improves performance on Linux quite a lot.

H2 Console and server mode: SSL is now disabled and TLS is used to protect against the POODLE SSLv3 vulnerability. The system property to disable secure anonymous connections is now "h2.enableAnonymousTLS". The default certificate is still self-signed, so you need to manually install another one if you want to avoid man in the middle attacks.

    JdbcDatabaseMetaData#supportsTransactionIsolationLevel(TRANSACTION_READ_UNCOMMITTED)
should return false

it now makes more sense to return a boolean for isLockedExclusivelyBy() from the lock()
method, to make it easier to reason about the atomic-ness of the operation

With the MVStore option, when using multiple threads that concurrently create indexes or tables, it was relatively easy to get a lock timeout on the "SYS" table.

With the MVStore option, when using multiple threads that concurrently create indexes or tables, it was relatively easy to get a lock timeout on the "SYS" table.

MVStore: improved error messages and logging; improved behavior if there is an error when serializing objects.