Locate the section for your github remote in the .git/config file. It looks like this:
[remote "origin"]
fetch = +refs/heads/*:refs/remotes/origin/*
url = [email protected]:joyent/node.git
Now add the line fetch = +refs/pull/*/head:refs/remotes/origin/pr/* to this section. Obviously, change the github url to match your project's URL. It ends up looking like this:
[remote "origin"]
fetch = +refs/heads/*:refs/remotes/origin/*
url = [email protected]:joyent/node.git
fetch = +refs/pull/*/head:refs/remotes/origin/pr/*
Now fetch all the pull requests:
$ git fetch origin
From github.com:joyent/node
* [new ref] refs/pull/1000/head -> origin/pr/1000
* [new ref] refs/pull/1002/head -> origin/pr/1002
* [new ref] refs/pull/1004/head -> origin/pr/1004
* [new ref] refs/pull/1009/head -> origin/pr/1009
...
To check out a particular pull request:
$ git checkout pr/999
Branch pr/999 set up to track remote branch pr/999 from origin.
Switched to a new branch 'pr/999'
git merge --ff-only origin/pr/4 # to ff to new addition