Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

/* -> /*- for copyright notices, minor format tweaks as necessary

Use __FBSDID().

add threadsafe version of inet_ntoa (inet_ntoa_r takes a buffer to fill)
this is used by some debugging functions

Add $FreeBSD$

Remove trailing whitespace.

Add inet_ntoa() and replace ARP's private routine with same.