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: I49f7f2a610aa586170b5f51089cb5479bf5d9b82
Reviewed-by: Janne Anttila <janne.anttila@digia.com>