spread the extern "C" { } magic pixie dust around. Python itself builds now

using a C++ compiler. Still lots and lots of errors in the modules built by
setup.py, and a bunch of warnings from g++ in the core.

Python/pystate.c

@@ -37,6 +37,10 @@ static PyThread_type_lock head_mutex = NULL; /* Protects interp->tstate_head */
 #define HEAD_LOCK() PyThread_acquire_lock(head_mutex, WAIT_LOCK)
 #define HEAD_UNLOCK() PyThread_release_lock(head_mutex)
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /* The single PyInterpreterState used by this process'
    GILState implementation
 */
@@ -552,4 +556,11 @@ PyGILState_Release(PyGILState_STATE oldstate)
 	else if (oldstate == PyGILState_UNLOCKED)
 		PyEval_SaveThread();
 }
+
+#ifdef __cplusplus
+}
+#endif
+
 #endif /* WITH_THREAD */
+
+