[R] 0/0, R segfaults

[Xing Qiu]

Hi, 

    I noticed that when I was conducting some calculation involving
finding correlation coeficients, R stopped abnormally. So I did some
research, and find out that 0/0 was the culprit.  For sure 0/0 is not
a valid expression, but R should give a warning, an error msg or NaN
instead of segmentation fault.

    I am using R 2.1.0 under Gentoo Linux. My GCC version is 3.3.5.

Xing