replace the existing checksummer with a modified version of the BSD
checksumming code. Add a flag to the "packet_info" structure to
indicate that a packet is the first fragment of a fragmented datagram,
so that the checksummers won't try to checksum those.
(It doesn't seem to add a lot of CPU overhead, so we don't introduce a
flag to disable it, yet. Further checks may be necessary to see whether
the overhead is just swamped by other overheads when scanning through a
capture dissecting all frames, or if it truly is negligible.)
Make the Boolean preference option controlling whether to make the
top-level protocol tree item for TCP display a packet summary static to
the TCP dissector (it doesn't need to be accessible outside the TCP
dissector).
svn path=/trunk/; revision=2751
Guy Harris