add unit/integrted tests for dpc

I checked with Hanfei. The detector pixel is always a square for DPC experiment.

> On Dec 1, 2014, at 3:44 PM, Thomas A Caswell <notifications@github.com> wrote:
> 
> In skxray/dpc.py:
> 
> > +    return phi
> > +
> > +
> > +def dpc_runner(start_point, pixel_size, focus_to_det, rows, cols, dx, dy,
> > +               energy, roi, bad_pixels, solver, ref, image_sequence, padding=0,
> > +               w=0.5, scale=True):
> > +    """
> > +    Controller function to run the whole DPC.
> > +
> > +    Parameters
> > +    ----------
> > +    start_point : 2-element list
> > +        start_point[0], start-searching point for the intensity attenuation.
> > +        start_point[1], start-searching point for the phase gradient.
> > +
> > +    pixel_size : integer
> Everywhere else, we let pixel_size be a 2 tuple because pixels are not always square.
> 
> —
> Reply to this email directly or view it on GitHub <https://github.com/Nikea/scikit-xray/pull/177/files#r21117920>.
> 

--
Best Regards,

  Cheng Chang 
  Computer Engineering, Stony Brook University
  Computer Science Group, Computational Science Center, Brookhaven National Laboratory
  Tel：(001) 631-885-4922