Prevent ADL from finding other dispatch functions or types. Required for #2094.

Richard Smith.

[SVN r57605]

include/boost/exception/exception.hpp

@@ -303,7 +303,7 @@ boost
         struct
         enable_error_info_return_type
             {
-            typedef typename enable_error_info_helper<T,sizeof(dispatch((T*)0))>::type type;
+            typedef typename enable_error_info_helper<T,sizeof(exception_detail::dispatch((T*)0))>::type type;
             };
         }