Automatically use latest matching branch of adblockpluschrome for nightlies
Background
When basing of feature branches of off the current release branch which depends on further changes in dependent repositories you need to remember to also create a matching branch for you feature branch in adblockpluschrome to ensure that the nightly builds for your feature branch don't fail i.e. if eyeo/abpui/adblockplusui@release-N depends on eyeo/abpui/adblockpluschrome@release-N all feature branches of off eyeo/abpui/adblockplusui@release-N need a matching (matching in name) feature branch eyeo/abpui/adblockpluschrome off eyeo/abpui/adblockpluschrome@release-N.
As the author of the feature branch I may not be aware of the dependencies of the current release branch in which case my feature branch build will fail without an immediately obvious reason requiring me to debug the situation.
It would help if the nightly build machinery could figure that out for me instead.
What to change
Make the nightly build machinery automatically use the latest matching head in case there is no explicit matching branch in adblockpluschrome i.e. if eyeo/abpui/adblockplusui@release-N depends on eyeo/abpui/adblockpluschrome@release-N automatically use that branch for all feature branches based off eyeo/abpui/adblockplusui@release-N that don't have a matching feature branch in eyeo/abpui/adblockpluschrome.