raco setup install: add `--source' and `--binary' modes

These flags allow a package downloaded in "built" form to be
stripped to source or binary form, which allows a single catalog
to serve three kinds of installations.
distro-build: change `#:source?' config to mean source packages, too

Use `#:source-runtime?' to make only the run-time system have
source form, while packages are pre-built.