Freedesktop thumbnail icon support

[Fred Kiefer]

I just submitted support for Freedesktop thumbnail icons to NSWorkspace. 
They work wounderfull inside of GWorkspace, of course only when another 
application has already created them. You will only benefit from this 
support when Konqueror or another similar file manager is running on 
your desktop. Ah yes, you also have to switch thumbnails on with the 
user default value GSUseFreedesktopThumbnails, by default they are off.

The biggest problem implementing this was a bug in NSBitmapImagerep 
which I had to fix first. The second problem the know abnormally of our 
URL handling. The rest is just the same code I did mail around half a 
year ago.

Hope you like it

Fred