some demos broken

[vks]

This is due to the internal reorganization and should thus be easy to fix.

Original issue for #216: http://code.google.com/p/mpmath/issues/detail?id=176
Original author: https://code.google.com/u/Vinzent.Steinberg@gmail.com/

[fredrik-johansson]

Yep. 

Also, mandelbrot.py could just switch between fp/mp instead of mpmath/cmath.

Original comment: http://code.google.com/p/mpmath/issues/detail?id=176#c1
Original author: https://code.google.com/u/111502149103757882156/