Changes 0.7.2:
* Upgraded libpng to version 1.4.12.
* Upgraded zlib to version 1.2.7-optipng.
! Fixed the display of huge (4GB+) file/IDAT sizes on 32-bit platforms.
! Issued a proper error message if the output IDAT can't fit in 2GB.
  Acknowledged this limitation in the user manual.
  (Thanks to John Sauter for the report.)
! Fixed the output file cleanup that should occur after a write error.
* Added the option -debug and various undocumented debug features.
* Moved the PNG reduction module (opngreduc) to a separate sub-project.

(adam)