Don't complain about schema version if it doesn't match expected naming pattern

We have a schema naming like drupal-3.0-beta19. If you are using an external index with a totally different naming schema, the check version_compare($stats_summary['@schema_version'], 'drupal-3.0-beta3', '<=') will often fail and print an error in the admin interface.

We should check that the schema name matches the expected pattern before applying this check.