Add built-in database methods unit tests for testing the errors generated when sending the corresponding messages to invalid object identifiers
Restrict valid values for the `code_prefix` flag to single character atoms

This is necessary to ensure that we can always reconstruct the entity identifier from the internal entity prefix.
Fix bug when converting an internal entity prefix to the entity identifier
Fix previous fix for a bug when converting an internal entity prefix to the entity identifier
Merge branch 'master' into namespaces