The __frontend variable was introduced to address the needs
of alterator-mkimage module: list the images available in
one column, purge the builddir.

Looks like we should consider other cases with redirected
stdout (cron builds, piped calls, etc) like fundamentally
non-interactive and behave the same.

So commit 3a8af6b5's
description is wrong now; the current cleanup rules are:

- if CLEAN=0 or DEBUG>1, don't do it;
- if CHECK or REPORT is set, don't do it;
- otherwise if at least one of the following conditions is true:
  + there's more than one target being built in a row;
  + stdout was redirected (cronjob, alterator-mkimage...);
  + metaprofile directory is read-only
  ...then do a distclean.

If that doesn't suit your needs, describe the particular
situation please.

Thanks cas@ for wondering aloud whether greppable output
is unsupported with `make help'.

Yes, mkimage-profiles is now able to build VM disk images.
So far the support is pretty basic:

- a single hard drive image with a single partition/FS
- only stock root password is configurable
- LILO is hardwired as a bootloader

The resulting images tend to boot under qemu/kvm though.

Please see doc/vm.txt for the warning regarding additional
privileges and setup required.  This was started back in
February but I still hoped to avoid sudo/privileged helper
(and libguestfs is almost as undistributable as can be)...

Thanks:

- http://blog.quinthar.com/2008/07/building-1gb-bootable-qemu-image-using.html
- Alexey Morarash who reworked that as https://github.com/tuxofil/linsygen
- led@, legion@, vitty@, aen@ for providing advice and inspiration

bin/ prefix tried to become a permatemp(tm).  No way.

The output was still somewhat ragged in 80x24 terminal window
with fmt(1) which wasn't anticipating the word length difference
subsequent column(1) would have to cope with later on.

Thanks Loic Cattani for his shell columnizer implementation:
https://github.com/Arko/Columnize

These are better off in their own lib/help.mk