#555

Request to merge #555 into the master branch.
That's right.  It seems like a useful unit test to try convolving with an InterpolatedImage of the kernel.  Probably with `x_interpolant='nearest'` and with the `real_space=True` option to `Convolve`.  It's not likely that this would be faster than the numpy calculation you have here, so I'm not recommending changing the implementation code.

The other suggestion was that it might be easier for the user to supply the kernel as an Image rather than as a numpy array, since this would clear up all the convention issues w.r.t. [y,x] and y increasing up, etc, which otherwise are a bit confusing, as you discovered.