'make release' should tag the commit

[tartley]

As is described in README-hacking

• Specifically, tag with the current value of __version__. Fail if that tag already exists.
  Possibly we should be creating annotated tags (see below):

  git tag -a -m "" $version
  

• Push the tag to origin. To do this for a commit which is already pushed, we might need::

  git push --follow-tags
  

  --tags pushes all tags on every branch, which is probably not desired. e.g. some will be private development status, some might be on distant or unreachable branches, etc.

  --follow-tags was designed to fix this, it only sends tags on ancestors of the current commit, and also only sends annotated tags.

[tartley]

this is a bad idea, tags should be written before doing the build