Some databases support transactional changes of the schema, but most don't.
Some don't update the schema metadata until the transaction ends.
To workaround all of these issues, a lock table is created at the beginning of the schema bootstrap
and removed afterwards. Each statement is executed in auto-commit mode. If there is a failure,
there is no alternative but to revert to the original data and try again.
git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@6215 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261
9cd707b76f