Add function to test headers agree.

Add a function to test that structure sizes match inside and outside of
OpenSSL.
diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index c08dbb3..042d93b 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -3324,6 +3324,14 @@
 			s->state == SSL3_ST_CR_FINISHED_A));
 	}
 
+void SSL_get_structure_sizes(size_t* ssl_size, size_t* ssl_ctx_size,
+                             size_t* ssl_session_size)
+{
+	*ssl_size = sizeof(SSL);
+	*ssl_ctx_size = sizeof(SSL_CTX);
+	*ssl_session_size = sizeof(SSL_SESSION);
+}
+
 int ssl3_can_cutthrough(const SSL *s)
 	{
 	const SSL_CIPHER *c;