NaN handling

[Ivan Vinogradov]

> <snip>
> NaNs are handled.

Throwing an exception would be nice in regular Python (non-scipy).

This works to catch NaN on OSX and Linux:

# assuming x is a number
if x+1==x or x!=x:
	#x is NaN

But is expensive as a precautionary measure.
Assert can be used for testing, if production code can be run with -0  
or -OO.