NOTE
You may not need local branches for all pull requests in a repo.
To fetch only the branch that you need, use Fetch and delete refs to GitHub pull request branches
If you do for some reason need all pull request branches locally, continue on.
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'