6194: add debugging to track the bug

Note that reflist is not an iterable but a flat list, so the added
debugging doesn't drain any delayed computations...

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps34@23449 4ae1f11a-8b86-4847-b8af-ab372f36d1fd