Merge branch 'master' into 'gtk3'

Most conflicts seemed to be simple enough. There were a lot of `append_text` to
`append` conversions for `Gtk::ComboBoxText`. The `PopUpCommon` class also saw
a lot of changes with non-trivial conflict resolutions.

rtgui/guiutils.cc

@@ -1246,11 +1246,16 @@ MyImageMenuItem::MyImageMenuItem(Glib::ustring label, Glib::ustring imageFileNam
     add(*box);
 }
 
-const RTImage *MyImageMenuItem::getImage()
+const RTImage *MyImageMenuItem::getImage () const
 {
     return image;
 }
 
+const Gtk::Label* MyImageMenuItem::getLabel () const
+{
+    return label;
+}
+
 
 BackBuffer::BackBuffer() : x(0), y(0), w(0), h(0), offset(0, 0), dirty(true) {}
 BackBuffer::BackBuffer(int width, int height, Cairo::Format format) : x(0), y(0), w(width), h(height), offset(0, 0), dirty(true)