I installed ros by running the following command:

~/rosinstall ~/ros http://ros.org/rosinstalls/boxturtle_base.rosinstall

then realized that I needed something from the pr2 stacks, so I tried:

~/rosinstall ~/ros http://ros.org/rosinstalls/boxturtle_pr2.rosinstall

and when it got to the pr2 stacks, I saw the following message:

Skipped '/home/dfseifer/ros/stacks/pr2_common'
Skipped '/home/dfseifer/ros/stacks/pr2_controllers'
Skipped '/home/dfseifer/ros/stacks/pr2_ethercat_drivers'
Skipped '/home/dfseifer/ros/stacks/pr2_gui'
Skipped '/home/dfseifer/ros/stacks/pr2_mechanism'
Skipped '/home/dfseifer/ros/stacks/pr2_power_drivers'
Skipped '/home/dfseifer/ros/stacks/pr2_robot'

I didn't see any info about how to remedy this on the installation
wiki, but the following command worked:

rm ~/ros/.rosinstall_source_uri

at which point it checked out all stacks, skipping the ones that were
already checked out. What is the correct procedure for this, and could
that be posted to the installation/rosinstall wikis somewhere?

-Dave