Log Message:
Changes 0.7.5:
* Upgraded libpng to version 1.6.10-optipng.
* Upgraded zlib to version 1.2.8-optipng.
! Fixed various build issues with libpng-1.5 and libpng-1.6.
* Allowed the handling of huge image files (> millions of pixels
  per row or column) to be independent of the libpng version.
+ Allowed the option -preserve to save the file ownership (UID/GID)
  on Unix.
! Fixed a build issue with Clang.
+ Added various enhancements to the configure script.