One test in data.cc crashes Octave 3.1.51

[John W. Eaton]

On 12-Aug-2008, Jaroslav Hajek wrote:

| Octave can use -NaN instead of NaN. I sent a simple fix some time ago,
| but apparently it was never applied, even though John stamped it "a
| reasonable thing to do" later in the same thread.
| See <http://www.nabble.com/Re%3A-automatic-Inf%2BNaN*i-conversion-p16895792.html>

I didn't mean to drop it.  It's applied now.

Thanks,

jwe