6663: RecentFiles.do_save() doesn't do XML escape

As John Ralls suggested, wrapped the path/db name in a CDATA
section upon writeout.

In DisplayState, instead of escaping _, tell gtk to ignore
the underline; add logging to help seeing ignored files.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps34@22773 4ae1f11a-8b86-4847-b8af-ab372f36d1fd