Thanks to everyone who has offered bug reports, patches, suggestions:
Alexey Akimov, Michele Bertoldi, Josiah Carlson, Tim Couper, Lisandro Dalcin, Markus Gritsch, Doug Hellmann, Charlie Hull, Richard Jones, Alexy Khrabrov, Gerald John M. Manipon, Kevin Manley, Paul Rudin, Sandro Tosi, Dominique Wahli.
Sorry if I have forgotten anyone.