Convert http links to https where possible in the source.
- use https for bug reporting
- in comments and docs, use https to refer to:
- www.gnu.org
- creativecommons.org
- translationproject.org
- mail.gnome.org
- www.perl.org
- www.ctan.org
- www.cl.cam.ac.uk
- www.ntg.nl
- cygwin.com
- www.ethnologue.com