Let the TLSv1_method() etc. functions return a const SSL_METHOD
pointer and make the SSL_METHOD parameter in SSL_CTX_new,
SSL_CTX_set_ssl_version and SSL_set_ssl_method const.

ssl/s23_clnt.c

diff --git a/ssl/s23_clnt.c b/ssl/s23_clnt.c
index 8bac26c..045a953 100644
--- a/ssl/s23_clnt.c
+++ b/ssl/s23_clnt.c
@@ -63,10 +63,10 @@
 #include <openssl/objects.h>
 #include <openssl/evp.h>
 
-static SSL_METHOD *ssl23_get_client_method(int ver);
+static const SSL_METHOD *ssl23_get_client_method(int ver);
 static int ssl23_client_hello(SSL *s);
 static int ssl23_get_server_hello(SSL *s);
-static SSL_METHOD *ssl23_get_client_method(int ver)
+static const SSL_METHOD *ssl23_get_client_method(int ver)
 	{
 #ifndef OPENSSL_NO_SSL2
 	if (ver == SSL2_VERSION)