setup: remove misc/make-version.py and invoke "darcsver" from the pyutil library

setup: remove misc/make-version.py and invoke "darcsver" from the pyutil library
misc/make-version.py has a limitation which prevents it from generating version
stamps from our current darcs history.  This limitation has been fixed in
pyutil's "darcsver".  Rather than copy the fix from there to
misc/make-version.py, I'm making it so that you have to install pyutil if you
want to automatically generate _version.py files from the current darcs
history.