merge/rebase in perlgit; also lulz

I have just pushed 961bfa8, which describes when and how to merge or rebase
work before pushing to perl5.git.  I would appreciate if other committers would
review it for accuracy and clarity.

In an attempt to produce a "can't make non-ff push" error, I accidentally
introduced a completely pointless commit, and then another to revert it.  I
apologize.  It's actually a bit funny, though.

While re-reading perlgit.pod to make these changes, I made a few cleanup
commits (a few sections were duplicated within the document!).  Then, to get
the error, I decided to move my head back a few commits so simulate work
against an old blead.  Unfortunately, I moved it back just as many commits as I
hade made while cleaning up, and the push worked.  Lesson learned:  next time,
simulate against my own darn projects.

-- 
rjbs

• merge/rebase in perlgit; also lulz by Ricardo Signes