Add tables of "conversation" dissectors, which are associated with

Add tables of "conversation" dissectors, which are associated with
particular protocols, and which keep track of all dissectors that could
be associated with conversations using those particular protocols - for
example, the RTP and RTCP dissectors could be assigned to UDP
conversations.

This is for future use with UI features allowing the dissector for a
given conversation to be set from the UI, to allow

	1) conversations between two ports, both of which have
	   dissectors associated with them, that have been given to the
	   wrong dissector to be given to the right dissector;

	2) conversations between two ports, neither of which have
	   dissectors associated with them, to be given to a dissector
	   (RTP and RTCP, for example, typically run on random ports,
	   and if you don't have, in a capture, traffic that would say
	   "OK, traffic between these two hosts and ports will be RTP
	   traffic", you may have to tell Ethereal explicitly what
	   protocol the conversation is).

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@2848 f5534014-38df-0310-8fa8-9805f1628bb7