The contains method for a Patch didn't use the picker to determine how far away from the patch the contains
method should go.  I believe that without this, the user had to place the mouse exactly on the stem of an arrow,
for example, and that's hard.  There needed to be some fuzz around the arrow stem in order to make the picking
easier.

NOTE that this patch may not be entirely correct, because I think I think that get_picker() returns something in
points, and that should be converted to pixels.  But it works well enough for me to ignore that.