Remove all trailing spaces

No real changes, just clean up sources by removing trailing spaces from
all the non-generated files.

This should hopefully avoid future commits mixing significant changes
with insignificant whitespace ones.

interface/wx/popupwin.h

@@ -38,7 +38,7 @@ public:
       Default constructor
     */
     wxPopupWindow();
-    
+
     /**
       Constructor
     */
@@ -125,5 +125,5 @@ protected:
        else but direct call to Dismiss().
     */
     virtual void OnDismiss();
-    
+
 };