Just add rows via the combobox's model, which should work with
both gtk2 and gtk3, instead of using the gtk_combo_box_append_text()
convenience API (which was renamed to gtk_combo_box_text_append_text()).
Fixes compilation against gtk3 (there was a typo in the list store
variable name, spotted by Markus Vartiainen).
f90b8bdfa0