New ctrl to set current certificate.

New ctrl sets current certificate based on certain criteria. Currently
two options: set the first valid certificate as current and set the
next valid certificate as current. Using these an application can
iterate over all certificates in an SSL_CTX or SSL structure.
diff --git a/ssl/ssl_locl.h b/ssl/ssl_locl.h
index c493f7e..fd6b883 100644
--- a/ssl/ssl_locl.h
+++ b/ssl/ssl_locl.h
@@ -999,6 +999,8 @@
 int ssl_cert_add0_chain_cert(CERT *c, X509 *x);
 int ssl_cert_add1_chain_cert(CERT *c, X509 *x);
 int ssl_cert_select_current(CERT *c, X509 *x);
+int ssl_cert_set_current(CERT *c, long arg);
+X509 *ssl_cert_get0_next_certificate(CERT *c, int first);
 void ssl_cert_set_cert_cb(CERT *c, int (*cb)(SSL *ssl, void *arg), void *arg);
 
 int ssl_verify_cert_chain(SSL *s,STACK_OF(X509) *sk);