New issue 611: Incorrect docstrings in plot_window.py
The docstrings for SlicePlot, ProjectionPlot, OffAxisSlicePlot and OffAxisProjection say
that the center defaults to the maximum density cell, but in fact it looks like they
default to the center of the domain. I'm filing an issue for this rather than just
fixing it myself because I'm not sure what people behavior is "right."