In py3k, imports are absolute unless using the "from . import" syntax.
This commit also solves a recursive import between Image, ImageColor, and
ImagePalette by delay-importing ImagePalette in Image.
I'm not too keen on this commit because the syntax is ugly. I might go back
and prefer the prettier "from PIL import".
Most of the differences are in tobytes/tostring naming and expected
behavior of the bytes() constructor. The latter was usually easy to fix
with the right bytes literal.
This is a good preview of what will have to happen in the Python 3 code.
