test-bus fails when built for Windows with CMake

On !23 (merged), @rhabacker wrote:

 2/20 Test  #2: test-bus .........................***Failed    5.70 sec

This is apparently reproducible on Windows 7, on Windows 10, and when cross-compiling under Linux and running the tests with Wine.

test-bus is large and complicated so I'm not really surprised. !1 (merged) breaks it into smaller pieces: it would be interesting to see which of them fail.