Although I will apply a simple bugfix for this, it brings up a question I have wanted to ask for some time:
Would it not make more sense for the backends to simply not stroke the patch boundaries if one specifies 'None' as the edgecolor? As it is, when we don't actually need edges, the backend is doing twice the work it needs to; and in the case of postscript, outputting a file twice as large as necessary (apart from the constant overhead). In addition, unnecessary boundary lines may make patches slightly larger than intended. An alternative way to say that we don't want edges drawn would be to specify zero width, and then let the backends interpret this as "do not draw" rather than "draw minimum width". This behavior could be added one backend at a time with little disruption, I suspect.