On Windows, make PyErr_Warn an exported function again.

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 2.5 release candidate 1?
 Core and builtins
 -----------------
 
+- On Windows, the PyErr_Warn function is now exported from
+  the Python dll again.
+
 - Bug #1191458: tracing over for loops now produces a line event
   on each iteration.  Fixing this problem required changing the .pyc
   magic number.  This means that .pyc files generated before 2.5c1

Python/errors.c

@@ -664,7 +664,7 @@ PyErr_WarnEx(PyObject *category, const char *message, Py_ssize_t stack_level)
 
 #undef PyErr_Warn
 
-int
+PyAPI_FUNC(int)
 PyErr_Warn(PyObject *category, char *message)
 {
 	return PyErr_WarnEx(category, message, 1);