Update ping(8) code and manpage to the newest ones from FreeBSD.

Update ping(8) code and manpage to the newest ones from FreeBSD.
Besides many small fixes this brings in some new features:

  * -D to set Don't Fragment bit
  * -G, -g and -h for sweeping pings
  * -M for using ICMP_MASKREQ or ICMP_TSTAMP instead of ICMP_ECHO
  * -o to exit successfully after receiving one reply packet
  * -W to set time to wait for a reply for each packet sent
  * -z to set TOS

Significant part of diff not related to the new features is coming
from reordering command line options into alphabetic order.

Obtained-from: FreeBSD