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/cshelp.h

@@ -257,8 +257,8 @@ public:
             Button position.
             If ::wxDefaultPosition is specified then a default position is chosen.
         @param size
-            Button size. 
-            If ::wxDefaultSize is specified then the button is sized appropriately 
+            Button size.
+            If ::wxDefaultSize is specified then the button is sized appropriately
             for the question mark bitmap.
         @param style
             Window style.