Fix the tutorial to make it work with python 32 and 64 bit.

gh-1508 fix make it work with only 32 bit python, before it was working only with 64 bit python. This one make it work with both.

NEWS.txt
- Fix to the tutorial (reported by Jason Yosinski and Ilya Dyachenko)
- Raise better error related to pydot bug (reported by Jason Yosinski and Ludwig Schmidt-Hackenberg) gh-1412

fix gh-1412