Fetch fixes

Refactored fetch_template() into fetch_stage3() and fetch_portage()

- The stage3 and portage tarballs are no longer unpacked in /var..
- Provide more flexibility with the portage setup (add $PORTAGE_SOURCE)

various small improvements/fixes/changes:
- use bashisms instead of calling external programs
- lowercase and make local variables that were only used inside a function.
- make downloading more verbose
- stop depending on bz2 compression
- remove redundant output suppresion
- remove redundant {} in variable expansion
- fix password handling (no more easily guessed default passwords)

etc.