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/s3_lib.c b/ssl/s3_lib.c
index 5c8aa13..ed50be1 100644
--- a/ssl/s3_lib.c
+++ b/ssl/s3_lib.c
@@ -3431,6 +3431,9 @@
 	case SSL_CTRL_SELECT_CURRENT_CERT:
 		return ssl_cert_select_current(s->cert, (X509 *)parg);
 
+	case SSL_CTRL_SET_CURRENT_CERT:
+		return ssl_cert_set_current(s->cert, larg);
+
 #ifndef OPENSSL_NO_EC
 	case SSL_CTRL_GET_CURVES:
 		{
@@ -3937,6 +3940,9 @@
 	case SSL_CTRL_SELECT_CURRENT_CERT:
 		return ssl_cert_select_current(ctx->cert, (X509 *)parg);
 
+	case SSL_CTRL_SET_CURRENT_CERT:
+		return ssl_cert_set_current(ctx->cert, larg);
+
 	default:
 		return(0);
 		}