Add check for `pcolor` and `contour` along with similar plots

It would be nice to have the same type of checking for calls to `pcolor` and its associated brethren.  I am not sure if this would be reliable enough as I believe that `pcolor` plots are stored as a set of polygons and it might be neither fast or accurate enough to be reliable.  Even more difficult might be consistently comparing contours (stored as lines I believe).
