[Rd] Accuracy of dnorm (PR#8586)

[marco.vezzoli@st.com]

Full_Name: Marco Vezzoli
Version: 2.2.0 2.1.0 2.0.0
OS: Solaris, Windows, Linux
Submission from: (NULL) (57.78.11.38)


The dnorm functions yield a wrong value when the standard deviation is near to
1e-1
e.g.
> dnorm(0,mean=0.04,sd=0.3)
[1] 1.318039

this error is consistent in various version and os.