Comment 7 for bug 1082391

It turned out to be surprisingly simple. The hardest part is to pick a name for it, but the existing convention (globalRect, Children) seems to be to use identifiers with capital names as these don't occur as "real" GtkWidget GObject properties. So I picked BuilderName for now, but I'm open to changing this.

Not a branch for now, as this adds new tests, and this depends on https://code.launchpad.net/~pitti/autopilot-gtk/add-tests/+merge/171036 (which is in turn blocked by https://code.launchpad.net/~pitti/autopilot-gtk/testsuite/+merge/170607). To avoid having to do excessive branch surgery, I keep this as a patch for now.