pipelines: give it 1 minute

Makefile: use file targets more, results in incremental building Less work to do when only some files get changed, but more work when building from scratch. But, multiple compilers can run in parallel.

Makefile: split .PHONY declaration

coffee: update compiler to 1.12.7, recompile

provision: it's probably safe to forget about Python 2.6 in 2017

provision: target newer Nginx versions (>1.9.5 in this case)

provision: use become instead of sudo

pipelines: install Mercurial to check builds and SRI Was lost after provision tests were removed from pipelines.

pipelines: switch to Xenial, use Ansible from distro repos

Make: use npm update for devel target package.json says we want coffee-script >= 1.6.1, so that's what `make devel` should install (the newest version): since .js source is tracked, there's no risk of running into breaking changes in coffee-script outside of test environment. But running into such changes during tests is OK and even potentially desirable.