configure.in requiring GTK to be 2.4 or greater means that Wireshark
tries to support any version of GTK starting with 2.4.
(Any code requiring a feature only available in later GTK versions is
#ifdef'd to be compiled only if Wireshark is being built with that
version or newer. In general, if this is done, alternative code should
be provided which compiles and works with the earlier GTK version).
So: if a function was implemented as of GTK 2.16, that means that any
Wireshark build on a system with an earlier GTK version will fail trying
to use that function. (Note that GTK 2.4 is [much] older than Gtk 2.16).
For example: my fairly up-to-date Fedora 10 system has Gtk2 2.14.7....