git again

[Oliver Kiddle <okiddle@xxxxxxxxxxx>]

I've cleaned up the duplication in the zsh-development-guide regarding
git usage and workflows. I'm not posting a patch because I think it'd be
better to discuss the content as it now stands than to pick over the
changes (That is, if further discussion is necessary which I can't say
I'm enthused by).

As confirmed with Peter, the intention is to keep things as unchanged as
possible from CVS for now. This means manual ChangeLog updates (though
not as a separate commit).

With this in mind, I've simplified the git branch usage written by Phil
to recommend git merge --squash. Note to git newcomers, this is still a
useful approach to follow: I use local branches even for fairly trivial
changes and check in regularly at intermediate states; often as a way to
push changes between Linux and Solaris.

A "Sharing Feature Branches" section can be added later once we start doing
that for non-trivial changes.

Anyway, I'll leave this for a week or so and then we can look at making
the actual switch.

Oliver