recent changes to the core solver.  Also added support for the nuclear norm
regularization and cache refinement options.

option to zero pad the borders of the output to it's easier to filter.

the separation oracle once the cache based refinement starts.

the entire image.  Also added a bunch of unit tests to cover the new behavior of
the filtering functions.

input to define the non-border area.

use nuclear norm regularization in their parameter estimation.

can't use the add_to or use_abs options with color images.

Thanks to Volker Härtel for finding this.

optimizations are enabled "warning: assuming signed overflow does not occur
when assuming that (X + c) < X is always false"

rather than converting to HSI and filtering just the I channel.  Also, the
spatially_filter_image_separable_down() routine now only allows grayscale
output images.