Environment variables

• QUILT_PRIMARY_PACKAGE_DIR - path to quilt_packages directory, where build and install products go (e.g. /SOME/PATH/TO/quilt_packages/)

• QUILT_PACKAGE_DIRS - colon-separated list of paths to search for Quilt packages (e.g. /foo/bar/quilt_packages:/boo/baz/quilt_packages)