Curl_input_negotiate: do not delegate GSSAPI credentials

This is a security flaw. See curl advisory 20110623 for details.

Reported by: Richard Silverman

lib/http_negotiate.c

@@ -243,7 +243,7 @@ int Curl_input_negotiate(struct connectdata *conn, bool proxy,
                                       &neg_ctx->context,
                                       neg_ctx->server_name,
                                       GSS_C_NO_OID,
-                                      GSS_C_DELEG_FLAG,
+                                      0,
                                       0,
                                       GSS_C_NO_CHANNEL_BINDINGS,
                                       &input_token,