Install all of the headers that belong in the top-level include directory.

Install all of the headers that belong in the top-level include directory.

Most of our headers should go only in the pcap subdirectory of the
top-level include directory, but we install some headers in the
top-level include directory for backwards compatibility; they just
include the relevant header from the pcap subdirectory.

We were only installing pcap.h; we also should install pcap-bpf.h and
pcap-namedb.h.