NaN handling

[Ivan Vinogradov]

> <snip>
> There are those of us that need NaNs in production code, so it
> would have to be something that could be configured.  I find
> that in my programs the places where I need to do something
> "exceptional" with a NaN are very limited.  The vast majority
> of the time, I need them to propagate quietly.

Our programming expectations may differ, but an option to catch NaNs as
an exception is a great idea.

Regards, Ivan.