wtap_wtap_encap_to_pcap_encap() to wiretap/pcap-encap.h. Include it
where it's needed; don't include other Wiretap headers where they're not
needed.
Include pcapng.h in pcapng.c, to declare the functions defined in
pcapng.c. Add some casts to squelch some warnings, and add to a comment
to indicate one of the problems.
svn path=/trunk/; revision=31960