How to rename a branch to master branch

[Bruno Coudoin <bruno coudoin free fr>]

Hi,

I have a development branch on GCompris that lasted 2 years. During that
time, I took care to port relevant master changes to my development
branch (named gcomprixogoo).

Now I would like to make this branch the master branch. I created a
gcompris-8-4 branch out of the master branch to keep it safe.

But in order to push my gcomprixogoo to master git refuses because it is
a NonFastForward update:
http://live.gnome.org/Git/Help/NonFastForward

It does not really make sense to rebase my devel branch on master, and
in trying I got so many conflicts that its not worth pursuing.

What is the recommended approach in this case ?

Bruno.