Exit from Ethereal by making the main loop exit, so that any quit

Exit from Ethereal by making the main loop exit, so that any quit
routines we register get called.

Register the "follow TCP stream" windows with "gtk_quit_add_destroy()",
so that, when Ethereal exits, they all get destroyed; this means that
their destroy callbacks get called, which means that they get to delete
their temporary files, so that, if you exit Ethereal without manually
closing the "follow TCP stream" windows, the temporary files don't get
left around.

Exit from Ethereal's "main()" function by calling "gtk_exit()", rather
than "exit()", so that we do whatever cleanup GTK+ requires.  (We used
to call "gtk_exit()" in the callback for the "File:Quit" menu item and
the "delete" callback for the main window, but we now just call
"gtk_main_quit()" so that we exit from the main loop.)

git-svn-id: http://anonsvn.wireshark.org/wireshark/trunk@1772 f5534014-38df-0310-8fa8-9805f1628bb7