I don't think this is a GTK problem.  Here is a very simple system that
just repeatedly calls `wipe_out' on an EV_TITLED_WINDOW, creates an EV_LABEL
and then calls {EV_TITLED_WINDOW}.extend, passing the label.  When executed,
the system uses more and more memory (in the heap).  It looks like maybe
the label is not garbage for some reason, though from my point of view it is,
and hence is not garbage collected until the final reclaim.

I tried this system with GTK+2.10.1 at home and it still would eventually
run out of memory (no difference from GTK+2.4).

Please look at this simple example and either tell me what dumb thing I'm
doing wrong or find and fix the problem for 5.7.