Make "proto_is_protocol_enabled()" and "proto_get_protocol_short_name()"
take a "protocol_t *" as an argument, so they don't have to look up the
"protocol_t" - this will probably speed them up considerably, and
they're called on almost every dissector handoff.
Get rid of a number of "proto_is_protocol_enabled()" calls that aren't
necessary (dissectors called through handles, including those called
through dissector tables, or called as heuristic dissectors, aren't even
called if their protocol isn't enabled).
Change some direct dissector calls to go through handles.
svn path=/trunk/; revision=8979
Guy Harris