Now we don't dump all the gory details onto thee
but rather log them handsomely and present only
the most important details by default; use DEBUG=1
and/or BUILDLOG=/path/to/file to tweak.

Also introduced IMAGEDIR and IMAGENAME.

The rest:
- ovz-smp is no more
- base-l10n pkglist (suggested by Alexander Kuprin)
- clean.mk:
  + fixed an oversight: the test result erroneously applied
    only to the first command of several ones that should be
    run iff build/ is a symlink
  + drop implicit rules (it's no C code)
- Makefile: more reasonable iso names
- image.in/Makefile: .disk/date too