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: Ie7e29bea0648a3e3b106951615ba05ec4beefb0e
Reviewed-by: Janne Anttila <janne.anttila@digia.com>