Change ecp_mul() prototype to allow randomization

(Also improve an error code while at it.)
diff --git a/tests/suites/test_suite_ecdh.function b/tests/suites/test_suite_ecdh.function
index 5bfd63d..ba35c76 100644
--- a/tests/suites/test_suite_ecdh.function
+++ b/tests/suites/test_suite_ecdh.function
@@ -27,8 +27,10 @@
                  == 0 );
     TEST_ASSERT( ecdh_gen_public( &grp, &dB, &qB, &rnd_pseudo_rand, &rnd_info )
                  == 0 );
-    TEST_ASSERT( ecdh_compute_shared( &grp, &zA, &qB, &dA ) == 0 );
-    TEST_ASSERT( ecdh_compute_shared( &grp, &zB, &qA, &dB ) == 0 );
+    TEST_ASSERT( ecdh_compute_shared( &grp, &zA, &qB, &dA,
+                                      &rnd_pseudo_rand, &rnd_info ) == 0 );
+    TEST_ASSERT( ecdh_compute_shared( &grp, &zB, &qA, &dB,
+                                      NULL, NULL ) == 0 );
 
     TEST_ASSERT( mpi_cmp_mpi( &zA, &zB ) == 0 );
 
@@ -70,9 +72,9 @@
     TEST_ASSERT( mpi_cmp_mpi( &qB.Y, &check ) == 0 );
 
     TEST_ASSERT( mpi_read_string( &check, 16, z_str ) == 0 );
-    TEST_ASSERT( ecdh_compute_shared( &grp, &zA, &qB, &dA ) == 0 );
+    TEST_ASSERT( ecdh_compute_shared( &grp, &zA, &qB, &dA, NULL, NULL ) == 0 );
     TEST_ASSERT( mpi_cmp_mpi( &zA, &check ) == 0 );
-    TEST_ASSERT( ecdh_compute_shared( &grp, &zB, &qA, &dB ) == 0 );
+    TEST_ASSERT( ecdh_compute_shared( &grp, &zB, &qA, &dB, NULL, NULL ) == 0 );
     TEST_ASSERT( mpi_cmp_mpi( &zB, &check ) == 0 );
 
     ecp_group_free( &grp );
@@ -107,8 +109,9 @@
                                    &rnd_pseudo_rand, &rnd_info ) == 0 );
     TEST_ASSERT( ecdh_read_public( &srv, buf, len ) == 0 );
 
-    TEST_ASSERT( ecdh_calc_secret( &srv, &len, buf, 1000 ) == 0 );
-    TEST_ASSERT( ecdh_calc_secret( &cli, &len, buf, 1000 ) == 0 );
+    TEST_ASSERT( ecdh_calc_secret( &srv, &len, buf, 1000,
+                                   &rnd_pseudo_rand, &rnd_info ) == 0 );
+    TEST_ASSERT( ecdh_calc_secret( &cli, &len, buf, 1000, NULL, NULL ) == 0 );
     TEST_ASSERT( mpi_cmp_mpi( &srv.z, &cli.z ) == 0 );
 
     ecdh_free( &srv );