travis: build leaves artifacts lying around

The current travis script and testing builds executable in a user-global space rather than locally to the package being tested and the tests then depend on this. This is sort of surprising so we should try not to do that.

Inspect the current Travis script and the testing build setup to see where executables are created and how the tests find them. The work is done when builds leave artifacts in the package's local space rather than a user-global space, and the tests still pass without relying on global artifacts.

Written by the indexing model from the issue text.