.travis:  Always run regression tests from `run_tests`
.travis:  Always run regression tests from `run_tests`

Previously disabled for merge commits to avoid some messiness with
package builds waiting for test outcomes before uploading packages,
and with the thinking that merged code has already been tested.
However:

- The messiness might be fixed now using the simple `after_success`
  key in `.travis.yml`

- This can catch bugs resulting from interactions between two merges,
  even when the original PRs individually passed; see [@kinsamanka's
  explanation][1]

[1]: https://github.com/machinekit/machinekit/issues/791#issuecomment-162167430

araisrobo/machinekit,strahlex/machinekit,araisrobo/machinekit,kinsamanka/machinekit,strahlex/machinekit,mhaberler/machinekit,araisrobo/machinekit,strahlex/machinekit,strahlex/machinekit,araisrobo/machinekit,ArcEye/MK-Qt5,araisrobo/machinekit,mhaberler/machinekit,kinsamanka/machinekit,strahlex/machinekit,mhaberler/machinekit,araisrobo/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,araisrobo/machinekit,kinsamanka/machinekit,strahlex/machinekit,araisrobo/machinekit,ArcEye/MK-Qt5,ArcEye/MK-Qt5,kinsamanka/machinekit,kinsamanka/machinekit,araisrobo/machinekit,mhaberler/machinekit,ArcEye/MK-Qt5,kinsamanka/machinekit,strahlex/machinekit,mhaberler/machinekit,mhaberler/machinekit,ArcEye/MK-Qt5,mhaberler/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,mhaberler/machinekit,ArcEye/MK-Qt5