 are slower and more accurate, because each
   new pixel is composed using an average of four neighboring pixels
   in the original image; this is sometimes also also called "antialiasing".
   Very fast color area mapping rotation is provided.

   The shear rotations are much faster, and work on images of arbitrary
   pixel depth, but they just move pixels around without doing any averaging.
   The pixRotateShearIP() operates on the image in-place.

   We also provide orthogonal rotators (90, 180, 270 degre