Removed all references to gtk objects from packet*.[ch] files. They now

Removed all references to gtk objects from packet*.[ch] files. They now
reference the protocol tree with struct proto_tree and struct proto_item
objects. That way, the packet decoding source code file can be used with
non-gtk packet decoders, like a curses-based ethereal, e.g. I also re-arranged
some of the information in packet.h to more appropriate places (like other
packet-*.[ch] files).

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@223 f5534014-38df-0310-8fa8-9805f1628bb7