Nuke trailing slashes from #223
Attempt to fix a race in build output test.

Naive sleep for half a second apparently does not work on travis
(systems under some/noticeable i/o load?).

Poll more frequently, and discard any responses that have
"HEAD is building" text, indicating the commit message has
not been loaded.

This should resolve the issue on travis without lengthening the
runtime of the test on faster systems.

See #221 for more information.