I think the new values are correct and am not able to reproduce the old values from the docs.
@astrofrog @kbarbary Agreed that the old example output from the aperture photometry docs 
is incorrect and the new values are OK?
```
In [9]: photutils.aperture_photometry(np.ones((100,100)), 10, 10, photutils.CircularAperture(1), method='exact')
Out[9]: 3.1415926535897931

In [10]: photutils.aperture_photometry(np.ones((100,100)), 10, 10, photutils.CircularAperture(1), method='subpixel')
Out[10]: 2.7599999999999998

In [11]: photutils.aperture_photometry(np.ones((100,100)), 10, 10, photutils.CircularAperture(1), method='center')
Out[11]: 1.0

In [12]: photutils.aperture_photometry(np.ones((100,100)), 10, 10, photutils.CircularAperture(3), method='center')
Out[12]: 25.0

In [13]: photutils.aperture_photometry(np.ones((100,100)), 10, 10, photutils.CircularAperture(3), method='subpixel')
Out[13]: 27.959999999999997

In [14]: photutils.aperture_photometry(np.ones((100,100)), 10, 10, photutils.CircularAperture(3), method='exact')
Out[14]: 28.274333882308134
```