dlRaw: new local contrast

Hi folks,

I know, it really took some time, but finally I can offer a new local contrast filter in dlRaw preview. It is modelled after this very nice gimp plugin and should give a similar result. However to improve the speed the implementation is not completely rigorous, but this shouldn't effect the quality. You can find it in the LAB tab as local contrast stretch.

Furthermore I added a color contrast filter. It was inspired from the technical side and not from the photography side. So I have to admit, I don't know if it will be usefull on many images. However, it helps to get nicer black and white images sometimes. Finally I could solve the problems with the Imagemagick integration on windows; now both versions rely on the same code. So, don't hesitate to get the new dlRaw preview and have fun

greets mike