Restore files deleted in a previous MR
Restoring some files and functions that were deleted in MR 74 ( !74 (merged) ), then found to be needed, viz.:
- Undeleted glue/ldbd.py
- Undeleted glue/segmentdb/query_engine.py
- Undeleted glue/segmentdb/segmentdb_utils.py, then re-deleted 4 functions that are no longer used
All files were undeleted using git checkout 3c47fb6 -- glue/ldbd.py
and similar.