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/html/helpctrl.h

@@ -269,7 +269,7 @@ public:
     wxHtmlHelpDialog* GetDialog();
 
 
-    
+
 protected:
 
     /**