RobotLocomotion/drake — pull request #624 by blandry (2014-12-15 21:30:08+00:00)
Title: Fix to the spring gradients

Fixes the bug referenced here: https://github.com/RobotLocomotion/drake/issues/621. It had never been noticed because our tests use a 1dof urdf, so also adding a 7dof plant for better test converage in the future.