So that shell scripts do not blunder on after errors.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

Debian package creation - crude, probably violated the Debian policys
but it seems to work just fine...
some other changes.

Also Makefile tweaks to help improve things somewhat - decided to
read the Makefile manual after some 15 years to updated my make
grey cells somewhat.

New command in the gpio command - readall