Fixing two issues with non-intrusive exception cloning support.

[SVN r72924]

include/boost/exception/exception.hpp

@@ -132,7 +132,17 @@ boost
             }
         };
 
+#if defined(__GNUC__)
+# if (__GNUC__ == 4 && __GNUC_MINOR__ >= 1) || (__GNUC__ > 4)
+#  pragma GCC visibility push (default)
+# endif
+#endif
     class exception;
+#if defined(__GNUC__)
+# if (__GNUC__ == 4 && __GNUC_MINOR__ >= 1) || (__GNUC__ > 4)
+#  pragma GCC visibility pop
+# endif
+#endif
 
     template <class T>
     class shared_ptr;