scan code for required gtk version

[Dan McMahill <mcmahill mtl mit edu>]

Is there a way to scan ones source code automatically to determine the
minimum required version of gtk and also glib?  The reason I ask is I've
been involved in a project that doesn't really use lots of the most
cutting edge features and in general, we only want to bump the required
version in cases where there is some really motivating reason to do so.
 That said, I also don't want to maintain a whole bunch of different gtk
installs only for purposes of trying to see how far back I can go and
still build this other program.

Thanks
-Dan