added torsional_spring_damper to drakeURDF.xsd
Merge branch 'master' of https://github.com/RobotLocomotion/drake into urdf_fix
updated comments to reflect addition of torsional_spring_damper in drakeURDF.xsd
minor updates to urdf spec
first pass at urdf parser and force element implementation for torsional springs
Merge branch 'master' of https://github.com/cmmccann/drake into torsional_spring
added torsional_spring_test.URDF
Merge branch 'master' of https://github.com/cmmccann/drake
torsional spring parsing works.  but test case fails
updating torsional spring test
fixed torsional spring.  passes unit test.  simulation looks right
respond to Robin's code review
Merge pull request #196 from cmmccann/torsional_spring

Torsional spring