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: I4a192ef6266d3e1a0c2c81679b7fa7a3658ac34c
Reviewed-by: Janne Anttila <janne.anttila@digia.com>