regenerate HTML versions of man pages (#147)

Use man2html-1.6-7.g on current git master branches as follows:

man2html -h -M /cgi-bin/man/man2html \
../tcpdump/tcpdump.1 > tcpdump_man.html

man2html -h -M /cgi-bin/man/man2html \
../libpcap/pcap.3pcap > pcap3_man.html

vim tcpdump_man.html pcap3_man.html # remove Content-type header