Use color to report the final test result, even when running in parallel

After the tests are run there is no more parallelism, so it should be less
likely that the control characters will introduce wierd artifacts.

src/lib/test.rs

@@ -171,8 +171,9 @@ fn run_tests_console_(opts: &test_opts, tests: &test_desc[],
 
     st.out.write_str(#fmt("\nresult: "));
     if success {
-        write_ok(st.out, st.use_color);
-    } else { write_failed(st.out, st.use_color); }
+        // There's no parallelism at this point so it's safe to use color
+        write_ok(st.out, true);
+    } else { write_failed(st.out, true); }
     st.out.write_str(#fmt(". %u passed; %u failed; %u ignored\n\n",
                        st.passed, st.failed, st.ignored));