Ignore test_log_functions test for now

It fails under valgrind

Author: marijnh

src/test/stdtest/math.rs

@@ -36,6 +36,7 @@ fn test_angle() {
 
 
 #[test]
+#[ignore]
 fn test_log_functions() {
     assert ln(1.0) == 0.0;
     assert log2(1.0) == 0.0;