dagop: raise ProgrammingError if stopdepth < 0
revset.py should never send such a value.
make: templatize Debian build target a la
e63dfbbdbd07
make: add Ubuntu Zesty docker targets (.deb and ppa)
Zesty Zapus was released on 2017-04-13 and will be supported until 2018-01.
docker: install less as a build-time dependency in deb-based distros
It's needed since
387a76cac28e, otherwise dpkg-checkbuilddeps errors out.