TODO for arpsend

Port to other platforms; stop ignoring most of what autoconf learns.
(Although the arpsend build process is autoconf-based, at
this time arpsend ignores almost everything autoconf discovers
about your system.)

If you specify a target IP address of 255.255.255.255, you are warned
that this is the IP limited broadcast address (correct), but then also
warned it is an IP experimental (Class E) address (wrong).
And you are also warned it is on the loopback network (wrong). 
Fix the warnings.