Use TLS for the PyThreadState pointer instead of a field on Connection; this allows a Connection to be used safely in multiple threads concurrently
diff --git a/src/ssl/ssl.h b/src/ssl/ssl.h
index e8d3e93..9cf0186 100644
--- a/src/ssl/ssl.h
+++ b/src/ssl/ssl.h
@@ -14,6 +14,7 @@
 #define PyOpenSSL_SSL_H_
 
 #include <Python.h>
+#include <pythread.h>
 #include "context.h"
 #include "connection.h"
 #include "../util.h"
@@ -45,6 +46,10 @@
 
 #define ssl_API_pointers          2
 
+#ifdef WITH_THREAD
+extern int _pyOpenSSL_tstate_key;
+#endif /* WITH_THREAD */
+
 #ifdef SSL_MODULE
 
 extern ssl_Context_New_RETURN    ssl_Context_New    ssl_Context_New_PROTO;