Commit 657c0bf6 has silently added use/bootloader
to the base use/install2 target thus breaking
experimental distro/netinst; it seems better to
require *a* bootloader in the target that's been
specifically designed to cover the common case
(thus linked to by +installer shortcut) but still
to have our base lightweight and flexible.

This doesn't hurt the actual distros as these use
+installer of course.