Blur operation does not Blur drawn elements

[lucastarche]

For instance, if blurring over an ellipse, the colour which should be present is not there. Example:

[RealKC]

Two things:

• this applies to Pixelate as well
• this doesn't apply when saving the surface to a file

I don't really know what to do :S

[RealKC]

With #7, this issue is a lot more visible and more easily replicable.

I still don't know how this would be fixed though.