another open=>io.open change, as John advised

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21720 4ae1f11a-8b86-4847-b8af-ab372f36d1fd
6544: add warning if place on event is missing by using proxies sequence

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/trunk@21724 4ae1f11a-8b86-4847-b8af-ab372f36d1fd