improve error message for  parsing errors.
improve error message for  parsing errors.

spaghetti-/rosdep,alessandro-aglietti/rosdep,sorki/rosdep,allenh1/rosdep,aymanim/rosdep,georgepar/rosdep,georgepar/rosdep,spaghetti-/rosdep,aymanim/rosdep,alessandro-aglietti/rosdep,wkentaro/rosdep,allenh1/rosdep,sorki/rosdep,ros-infrastructure/rosdep,wkentaro/rosdep,ros-infrastructure/rosdep