Bug#1107483: The manpages and the infopages of pngcrush should mention the overwrite option

[Peter Müller]

Package: pngcrush
Version: 1.8.13-0.1

In the man pages (man pngcrush) and the info pages (info pngcrush) do not 
mention the overwrite option. Opposed to this, the built-in help of pngcrush 
(pngcrush --help) shows the option “-ow (Overwrite)”.  Please complete the man 
and info pages.