Documentation + base.rosinstall update

I encountered two errors following the directions to build a ROS underlay:
http://ros.org/doc/groovy/api/catkin/html/adv_user_guide/underlay.html
1) The URL for the rosinstall file was wrong
2) Some of URI's in the rosinstall file were out of date / broken.

As everything in the rosinstall file is for groovy, perhaps it'd also be a good idea to rename base.rosinstall -> groovy_base.rosinstall or something similar?