modify (semi-revert) 21728/21729 open=>io.open change, for Windows

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps40@21731 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
revert 21728/21729 open=>io.open change, for Windows

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps40@21732 4ae1f11a-8b86-4847-b8af-ab372f36d1fd