Move forward reproducible builds

Description of the project: How can we assess that a given binary package was indeed produced by the source it claims to be coming from? By enabling independent parties to create a byte-for-byte identical packages from the same source, the ReproducibleBuilds project will enhance trust in Debian, and free software in general. Very good progress has been made over the course of the past year, but several general and particular problems remain. Some issues require careful examination, getting deep down the rabbit hole to understand the source of variations, and ingenuity to come up with fixes. If possible the issues should be fixed at the toolchain level and thus will a lot of packages at once.