`Stats.sum` doesn't handle NaNs, infinities and overflow correctly

[g3xzh]

Like @huonw has put it here: Stats.sum doesn't handle "extreme" values nicely.

[g3xzh]

I think I will take this issue.
@huonw, it will be more than a pleasure, if you mentor me through this too.

[g3xzh]

@huonw ,
How about this for handling summation overflow?
http://stackoverflow.com/a/199455 (the addition_is_safe function).

[huonw]

@g3xzh I don't see any reason to depart from the algorithm that Python is using: http://bugs.python.org/file10357/msum4.py

[g3xzh]

@huonw - 10x. I hope I will finish working on it this week.

[huonw]

@g3xzh any progress? :)

[g3xzh]

@huonw there was some. However, I cannot compile it (rustc is broken on my machine) and because of the exam season I could not continue working on it. :-\

[huonw]

If someone else is interested, is it ok if they work on it?

[g3xzh]

I don't mind. My last exam, this semester, is in the 13rd, though. :)