ENH: reduce overhead of probs check of choice

Use kahan_sum as multinomial does.
Closes gh-4188
MAINT: regenerate with cython 0.20 and fix a warning it emits

Fixed warning is "Non-trivial type declarators in shared declaration".
Merge pull request #4213 from juliantaylor/choice-improv

improve random.choice performance and regen with cython 0.20