Next to the convenient environment setup and package build from git
guix environment -l .guix.scm
guix build -f .guix.scm
we can now also build other included packages
GUIX_PACKAGE_PATH=guix guix build mes@0.17
GUIX_PACKAGE_PATH=guix guix build nyacc@0.80.42
* guix/git/mes.scm: Move from .guix.scm, make a module.
* .guix.scm: Move from guix.scm, use it.
* build-aux/manifest.scm: Update location.
* build-aux/pre-inst-env.in: Support it.
* configure: Check for guix.
* build-aux/export.make: Export GUIX.
* GNUmakefile (update-hash): New target.
