Fix #727 and make wscript to generate tarballs like the revised ~/devel/make-tarball

Now tarballs lack the dotfiles and most contents of build/, but do properly include include/pivot.h, and the manual/HTML pages.

Changed dist, distcheck, and in repo builds to get a version from new function distname. distname uses string mangling on the output from git describe as a string taking a context. If git is indisposed the version will be taken from the VERSION file, which is not good for people working from checkout or bad CI jobs.

>>> # Python doctest type example
>>> dirname(ctx)
ntpsec-1.2.1-55-gd67df8b09-dirty