add unit/integrted tests for dpc

None the less, `scale is True` is not good python practice.  The case of
`scale == 1` _is_ a problem as most users would expect that to be a valid
'true' value.

On Tue Nov 25 2014 at 11:07:38 AM thegreatwall <notifications@github.com>
wrote:

> In skxray/dpc.py:
>
> > +        imx, imy = image_reduction(im, roi, bad_pixels)
> > +
> > +        # 1-D IFFT
> > +        fx = np.fft.fftshift(np.fft.ifft(imx))
> > +        fy = np.fft.fftshift(np.fft.ifft(imy))
> > +
> > +        # Nonlinear fitting
> > +        _a, _gx = dpc_fit(ffx, ref_fx, fx, start_point, solver)
> > +        _a, _gy = dpc_fit(ffy, ref_fy, fy, start_point, solver)
> > +
> > +        # Store one-point intermediate results
> > +        gx[i, j] = _gx
> > +        gy[i, j] = _gy
> > +        a[i, j] = _a
> > +
> > +    if scale is True:
>
> I defined the scale to be a bool variable. It's meaningful to supply True
> if you want to scale, False if not. I think it's not straightforward to
> supply other true-ish values (like 'apple') if you want to scale.
>
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> <https://github.com/Nikea/scikit-xray/pull/177/files#r20872662>.
>