* gnu/installer/parted.scm (root-user-partition?): New procedure.
(bootloader-configuration): Use it.
(user-partition-missing-modules, initrd-configuration): New procedures.
(user-partitions->configuration): Call 'initrd-configuration'.o
* gnu/installer.scm (not-config?): Rename to...
(module-to-import?): ... this. Add cases to exclude non-installer and
non-build (gnu …) modules.
(installer-program)[installer-builder]: Add GUIX to the extension list.