Somewhat localised game's version stuff to the Makefile. The Makefile

Somewhat localised game's version stuff to the Makefile.  The Makefile
uses a small shell script to construct a suitable version string
("dev-r1234").  If that doesn't work, make fails.  The version can of
course also be set as any make variable, which is what you'd do if the
script failed or it's the release time.  (Yeah, right...)

I'm not really happy with how it works, but I guess it does what I want:
intelligent versioning for development builds;  complains loudly enough
for someone to make the effort and actually update it;  makes (will
make) the NSIS script version aware in a simple fashion.

git-svn-id: https://s.snth.net/svn/neverball/trunk@1034 78b8d119-cf0a-0410-b17c-f493084dd1d7