Look up the IP Address by Hostname
- the name of the host.
This was included as a test of internet connectivity, to fail if
the node running R is not connected. It will also return
if BSD networking is not supported, including the header file
arpa/inet.h. This function is not available on Windows.
The IP address, as a character string, or
NULL if the call fails.
## Not run: nsl("www.r-project.org")