Introduce experimental new feature: GTK2 tree view based packet list

Introduce experimental new feature: GTK2 tree view based packet list

To use the GTK2 based packet list, define NEW_PACKET_LIST when compiling.
To do this with gcc, set the environment variable CPPFLAGS to
"-DNEW_PACKET_LIST" and re-run configure.

Many features do not yet work.  This work began with prototypes by Ulf
quite a while back.  I've put quite a bit of work into this so far and
as discussed with a few of the core team members at Sharkfest09 and it was
decided that it would be best to commit what I have so far to allow others to
help work on this.

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@28892 f5534014-38df-0310-8fa8-9805f1628bb7