since we have removed the synchronization from Database#lockMeta,
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

git-svn-id: http://h2database.googlecode.com/svn/trunk@5896 e6896862-9d19-0410-bfb3-e9fa5d50e656
Issue 581: When running in LOCK_MODE=0,
    JdbcDatabaseMetaData#supportsTransactionIsolationLevel(TRANSACTION_READ_UNCOMMITTED)
should return false


git-svn-id: http://h2database.googlecode.com/svn/trunk@5897 e6896862-9d19-0410-bfb3-e9fa5d50e656