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/gbsizer.h

@@ -82,7 +82,7 @@ public:
     //@{
     /**
         Adds the given item to the given position.
-        
+
         @return A valid pointer if the item was successfully placed at the
                  given position, or @NULL if something was already there.
     */
@@ -299,7 +299,7 @@ public:
     */
     bool SetSpan(const wxGBSpan& span);
 
-    
+
     wxGridBagSizer* GetGBSizer() const;
     void SetGBSizer(wxGridBagSizer* sizer);
 };