Log Message:
Update to 0.16 (leaf package):

* Introduce the MOUNT_{PACKAGES,PKGSRC,PKGSRCDIST}_DIR options in the
  configuration file, to use null mounts for them. By default neither
  of these directories will be mounted by default.

* Introduce the concept of 'targets done'. If the user tries to issue
  a 'base' target before the 'kernel' target an error message will be
  printed and an appropiate error code returned (just an example, it is
  done for all required targets). This is useful to avoid silly things
  like:

  [mklivecd kernel target was skipped here]

  $ mklivecd base
  $ mklivecd chroot
  $ mklivecd iso

  Obviously the 'iso' target failed because it couldn't find some
  required files.