IterativeParabolicTimeParameterization now ignores virtual joints.
When checking if all joints are single-DOF, it accepts multi-DOF joints only if they are
also virtual.
Removed check for multi-dof joints in iterative_time_parameterization.cpp.
Merge pull request #170 from ros-planning/time-param-ignore-virtual

IterativeParabolicTimeParameterization now ignores virtual joints.