FakeBrushChunk now has a fake Biomes.

Maybe someday we'll proxy the world's Biomes here and update them as the cursor moves?  Naaaah, too much mesh rebuilding.

src/mcedit2/editortools/brush/__init__.py

@@ -202,6 +202,7 @@ class FakeBrushChunk(object):
         self.dimension = world
         self.cx = cx
         self.cz = cz
+        self.Biomes = numpy.zeros((16, 16), numpy.uint8)
 
     @property
     def blocktypes(self):