fixed error on detecting that a given parameter was a ctypes array
python 3 fix of apple_hello_world sample

Better use "array.nbytes" that relying on len(array.data). As
array.data is a memory view in python3 that returns number of
elements instead of byte length (as it happen on 2.7 where data
is a buffer.
fix python3 amd_simple_convolution.py

- "b" prefix for opencl program string
- tweaks to make for a different image format in skimage.data.moon().
  Made more robust.