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/htmllbox.h

@@ -218,7 +218,7 @@ public:
             Window position.
             If ::wxDefaultPosition is specified then a default position is chosen.
         @param size
-            Window size. 
+            Window size.
             If ::wxDefaultSize is specified then the window is sized appropriately.
         @param n
             Number of strings with which to initialise the control.