python-imaging/Pillow — pull request #399 by tmccombs (2013-10-31 01:42:21+00:00)
Title: Closes #397. Fixed Viewer.show to return properly.

Viewer.show did not return a value, however ImageShow.show expected
Viewer.show to return a non-falsey value if successful. Therefor ImageShow.show
would continue to call multiple viewers.