Version.sh updates

Simplify version number chooser.

Don't warn about anything.

Look for most recent tag, count commits since then to the merge base
between this and origin/master. That's the subversion.  Then count
(local) commits since then and how many local files have been modified
to get the extra version.

Also the export-subst attribute should be against the version script
not the Makefile.

This was causing version.c to be rebuilt every time, even if the GIT
variables are properly set.  (Doh!)
Improve notification of tape type
Detect some other processor variants.