[lmi] GTK warnings

[Greg Chicares]

With the wx upgrade, I still have a few GTK warnings:

(lmi_wx_shared:79710): Gtk-WARNING **: 19:32:24.395: Drawing a gadget with 
negative dimensions. Did you forget to allocate a size? (node tab owner 
GtkNotebook)

(lmi_wx_shared:79710): Gtk-CRITICAL **: 19:32:24.402: 
gtk_box_gadget_distribute: assertion 'size >= 0' failed in GtkScrollbar

Would it be easy to prevent those? I conjecture that notebook
tabs might have a dimension of -1, perhaps due to a wx default
that's not explicitly expressed in 'skin.xrc', which says only:

  <object class="wxNotebook" name="input_notebook">
      <object class="notebookpage">
          <label>Plan</label>
          <object_ref ref="plan_panel"/>
      </object>
      <object class="notebookpage">

...and so on.