Allow imports from setup.py without triggering installation.

Also define versiondata constant for fetching up-to-date
version and date data.
setup.cfg should be ignored.
Reuse version and date data from setup.py.

This also keeps them fresh after more git commits.
Fix to allow launching make from other directory.

CURDIR always refers to the Makefile directory.
Make publish update gh-pages only in the local repository.

This is better since "git push" would then send updates to origin for both
master and gh-pages at the same time.