Selections work!

[Boudewijn Rempt]

Selections Work! Really! And gradients only fill the selected area! Yippee!
Of course, quite a bit of work remains to be done, and the implementation 
could be a little bit faster, but... Selections work! 

Now for all the little points mentioned in the design/todo I posted earlier. 
And... I am using pixel/setPixel for everything, as was Adrian in the 
gradient code, so that's a source of performance loss. I really feel there 
are problems were a good & fast pixel/setPixel are a better solution than
iterators, and we might look into improving that area. For instance, by 
removing the un-used locking.

But... We have selections of a kind again.