Harness: properly format negative zero

harness/assert.js

@@ -96,6 +96,10 @@ assert.throws = function (expectedErrorConstructor, func, message) {
 
 assert._toString = function (value) {
   try {
+    if (value === 0 && 1 / value === -Infinity) {
+      return '-0';
+    }
+
     return String(value);
   } catch (err) {
     if (err.name === 'TypeError') {

test/harness/assert-samevalue-zeros.js

@@ -18,6 +18,7 @@ try {
       '" was thrown.'
     );
   }
+  assert.notSameValue(err.message.indexOf('-0'), -1);
 }
 
 if (threw === false) {