Multipart id numbering sequence_by_type option requires that element names across types be unique

The sequence_by_type option in multipart_id_numbering.conf forces the numbering system to maintain a separate SERIAL sequence for each type having it set. Currently, if you set this on multiple types within a table (typical), the maximum value for each sequence is tracked using a combination table and element name (NOT type), which means if element names are reused across types the sequence separation fails.

This is confusing and should be changed such that type is included in the criteria used to track sequences.