Added option to perform reverse lookups of destination IPs

Upstream proxies may require the hostname for CONNECT requests.
A local DNS server can be configured to provide a reverse lookup
of the forward lookup cache. As a rough example, in bind9, an
authoritative in-addr.arpa zone can be created and updated using
a combination of tcpdump|sed|nsupdate such as:
(echo server 127.0.0.1;tcpdump -pnnlvi any "udp port 53" 2>/dev/null|sed -une 's/\([^ ]\+\) A \([0-9]\+\)\.\([0-9]\+\)\.\([0-9]\+\)\.\([0-9]\+\)/\nupdate add \5.\4.\3.\2.in-addr.arpa 86400 ptr \1\n\n/g;s/^[^\n]*\n//;s/\n\n[^\n]*$/\nshow\n/;s/\n\n[^\n]*\n/\n/gp')|nsupdate -v -k /etc/bind/Kin-addr.arpa.+157+10867.private