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/thumbbrowserbase.h

@@ -134,6 +134,12 @@ public:
     void scroll (int direction);
     void scrollPage (int direction);
 
+private:
+    void selectSingle (ThumbBrowserEntryBase* clicked);
+    void selectRange (ThumbBrowserEntryBase* clicked, bool additional);
+    void selectSet (ThumbBrowserEntryBase* clicked);
+
+public:
     void selectPrev (int distance, bool enlarge);
     void selectNext (int distance, bool enlarge);
     void selectFirst (bool enlarge);