Bump SaveVersion to 6

A generalisation can take a default - this enhancement is not backwards
compatible, so bump the SaveVersion to reflect this.
debian/control: Removed the dependencies upon wx2.8
regenerate_all.sh: Use 'git describe' to label current version
build_all.sh: 'make -j6' to speed up the build.
genmakeinst.sh: regenerate / make / install packages