Check for 'package://' syntax and warn once

URDFRigidBodyManipulator presently does not support the 'package://' syntax for
specifying mesh filenames. Rather than spam the user with a warning for each
mesh file, we now warn once per urdf that uses that syntax.
Re-enable building of urdf_collision_test

Also fixes the executable name in the usage message for urdf_collision_test.
Merge pull request #299 from avalenzu/fix-URDFRigidBodyManipulator-warnings

Fix urdf rigid body manipulator warnings