* Upgraded libpng to version 1.2.12-optipng [private]
* Implemented basic support for TIFF (grayscale, RGB and RGBA, uncompressed).
* Avoided the redundant trial when the search space is singular
(e.g. when running "optipng -o1 example.tif").
* Prevented accidental file corruption when using option "-log".
* Fixed (again) a small typo in the online help.
without losing any information. The idea has been inspired from pngcrush, and
is explained in detail in the PNG-Tech article: "A Guide to PNG optimization"
<http://www.cs.toronto.edu/~cosmin/pngtech/optipng.html>. The implementation
is carried forward in OptiPNG, which offers a faster execution per trial, and
a wider search space.
