Merged back combobox_darwin.m, rewrote it to use boundListboxArray() instead of creating a whole new object, and implemented what appears to be a fix for NSPopUpButton selection. Will delete the unneeded select(-1) code later and test again...
Checked to see if the previous commit worked after removing the leftover Combobox selectIndex() code; it does. Removed the dummy code from the Windows and GTK+ backends as well.