[C++-sig] Useless use of type attributes

[Philipp Thomas]

boost/python/detail/wrapper_base.hpp and boost/python/detail/exception_handler.hpp
needlessly uses type attributes in the forward declaration, which
prompts gcc 4.1 to warn with

 warning: type attributes are honored only at type definition

here's a patch to fix this:

--- boost/python/detail/exception_handler.hpp
+++ boost/python/detail/exception_handler.hpp
@@ -11,7 +11,7 @@
 
 namespace boost { namespace python { namespace detail {
 
-struct BOOST_PYTHON_DECL exception_handler;
+struct exception_handler;
 
 typedef function2<bool, exception_handler const&, function0<void> const&> handler_function;
 
--- boost/python/detail/wrapper_base.hpp
+++ boost/python/detail/wrapper_base.hpp
@@ -14,7 +14,7 @@
 
 namespace detail
 {
-  class BOOST_PYTHON_DECL wrapper_base;
+  class wrapper_base;
   
   namespace wrapper_base_ // ADL disabler
   {