t an
   arbitrary point (really, a line), both in-place and from source to dest.
   The interpolated shear is used on 8 bpp and 32 bpp images, and
   gives a smoother result.  Shear is used for the fastest implementations
   of rotation.

   There are three different types of general image rotators:

     a.  Grayscale rotation using area mapping
         - pixRotateAM() for 8 bit gray and 24 bit color, about center
         - pixRotateAMCorner() for 8 bit gray, about image UL corner
         - pixRotateAMC