Hi,
anonym just merged the branch for #9262 aka. "Port our ISO build
system to Jessie", so if you have an ISO build setup, you need to
upgrade it:
 * manual build system
   See the updated doc: 
https://tails.boum.org/contribute/build/#manual
 * Vagrant (untested)
   rake vm:destroy
   rm -r vagrant/.vagrant
   rake vm:up
Please report any issues to us :)
JFTR, our Jenkins ISO builders have been upgraded yesterday already.
Cheers,
-- 
intrigeri