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.

src/qt/checkbox.cpp

@@ -118,7 +118,7 @@ wxCheckBoxState wxCheckBox::DoGet3StateValue() const
 
     case Qt::Checked:
         return wxCHK_CHECKED;
-        
+
     case Qt::PartiallyChecked:
         return wxCHK_UNDETERMINED;
     }