We should test stable branches against stable branches only.
At some point we should automate the merges from dev->stable->release
and decide how to handle possible merge conflicts.

This is good enough for the time being.

Change-Id: Ie117ec0e488c740c0be01359912520d54c24248f
Reviewed-by: Janne Anttila <janne.anttila@digia.com>