Some GdkPixbuf Stuff

Included are two commits with pixbuf stuff.

Neither of the scaling methods use a pixbuf as a receiver, but since you're not manipulating the source pixbuf, I thought this was appropriate. Additionally, ```Scale()``` does not take an output pixbuf pointer as in the C version, but instead returns it. It seems weird to me that the GDK authors would have this inconsistency between ```gdk_pixbuf_scale_simple()``` and ```gdk_pixbuf_scale()```, but what do I know?