Supposedly you can use the "git rebase -i origin/master" command as described in the CONVENTIONS file. It doesn't seem to work on me, however; I get the message "Usage: /usr/bin/git-rebase [-v] [--onto <newbase>] <upstream> [<branch>]"; looking at my online documentation does not reveal a -i option. ^^
You probably need a newer git. People recommend using git HEAD and I haven't had problems with it so far.
cd ~/src
git clone git://git.kernel.org/pub/scm/git/git.git
cd git
make prefix=$HOME/apps all doc info
make prefix=$HOME/apps install install-doc install-info