Change FIXME in TODO and clarify its meaning.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@31230 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/arrstr.h

@@ -209,7 +209,7 @@ public:
   typedef int difference_type;
   typedef size_t size_type;
 
-  // FIXME: same in dynarray.h
+  // TODO: this code duplicates the one in dynarray.h
   class reverse_iterator
   {
     typedef wxString value_type;