[Bug 6413] Fix importing ProGen files

This isn't a perfect fix because it requires that the ProGen file is
encoded with CP437, which is guaranteed only in Version 3.21 and later.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21355 4ae1f11a-8b86-4847-b8af-ab372f36d1fd