Coalesce common dependencies in the dependency map

Right now, I have a task which depends on several other tasks, and some of
those depend on the same underlying tasks. An example of this would look
like:

   A
 /  |  \
B  |  C
 \  |  /
   D

I would expect the dependency map view to draw a line between B&D as well
as C&D, but this is not the case. Currently the view renders the example as:

   A
 /  |  \
B D C
|       |
D     D

I wouldn't expect there to be three copies of D in the map. Instead, I'd like both B&C to each have an arrow to a single copy of D. The way it's set up now, it is somewhat confusing to visualize all the dependencies, since there are multiple copies of multiple features in the graph.