[ptx] vigra included in sourcecode again

[alexandre jenny]

Hi,

I tried this version of vigra and impex with the 16 bits formats and
it works quite well. 

Alexandre


> Hi!
> 
> I decided to include the patched vigra headers + the enhanced 
> vigra image load/save routines completely into the source dir.
> 
> I don't like to force people to install libraries patched for 
> one program.
> 
> That means, no external vigra package is needed anymore.
> 
> ciao
>   Pablo
>