Log Message:
Changes 6.6.9.8:
* Fixed some cut-and-paste errors in new png.c code that caused PNG8
  reductions to fail.

Changes 6.6.9.8:
* Add various Option Flags, and fix option skip counts for plus forms
  of simple operators where plus form is the same as minus form.
  For example the incorrect counts produces a weird error, and posible
  future segmentation fault in a command like  convert rose: +border show:

Changes 6.6.9.7:
* Fix FX default for interpolation to Bilinear.
* Fix pixel interpolation for -draw image over (reference
  http://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=18612).
* Write the proper bKGD chunk value in grayscale PNG images (reference
  http://www.imagemagick.org/discourse-server/viewtopic.php?f=3&t=18624).
* Added Inverse method for Sparse Color Interpolation