Adding --system option to define the resulting image type to be a live system or a normal, non-live system.

This is the first step in conglomerating code for all hdd-ish
image types, independent of the partitioning scheme being used,
and adding future hdd-ish image types for virtualiziation software.

Adding support for ext4 for binary and chroot filesystem, including partial patch from Ben Howard <ben.howard@canonical.com> (Closes: #639298).

Adding kubuntu mode in order to have different defadefault hooks enabled for ubuntu and kubuntu (needed for #630088).

In order to be consistent with terminology used in debian-policy,
we've always tried to use the same names for the same things.

The repository option is one of the last things that were too
late in squeeze release cycle to be renamed in time.