overriding the use of the dpkg architecture for the livecd run.
* Differentiate between ARCH (the local architecture) and TARGETARCH,
so that builds of ubuntu-lpia continue to work on the i386 buildd.
* Pass ARCH by default from BuildLiveCD to livecd.sh; this should be
manually overridden on cross-arch buildds, instead of using dpkg.
* Update default suite in BuildLiveCD to intrepid, gutsy's a bit old.