EJB Timer database check

SourceForge Submitter: juanmartinez .
Hi.

The GeneralPurposeDatabasePersistencePlugin class
doesn't use SQLUtil when checking if the "TIMERS" table
exists.

This leeds to an error, since PostgreSQL stores
tablenames in lowercase - SQLUtil uses
DatabaseMetadata to do the right checks.

The attached fixes this problem by using SQLUtil.

Let me know if I can provide more information.
Juan