Respect assert.doesNotThrow message.

lib/assert.js

@@ -300,8 +300,12 @@ function _throws(shouldThrow, block, expected, message) {
   if (shouldThrow && !actual) {
     fail(actual, expected, 'Missing expected exception' + message);
   }
-
-  if (!shouldThrow && expectedException(actual, expected)) {
+
+  if (!shouldThrow &&
+      actual instanceof Error &&
+      util.isString(message) &&
+      expectedException(actual, expected) ||
+      !shouldThrow && actual && !expected) {
     fail(actual, expected, 'Got unwanted exception' + message);
   }
 

test/simple/test-assert.js

@@ -209,6 +209,13 @@ assert.throws(function() {assert.ifError(new Error('test error'))});
 assert.doesNotThrow(function() {assert.ifError(null)});
 assert.doesNotThrow(function() {assert.ifError()});
 
+try {
+  assert.doesNotThrow(makeBlock(thrower, Error), 'user message');
+} catch(e) {
+  assert.equal(e.message, 'Got unwanted exception. user message',
+               'a.doesNotThrow ignores user message')
+}
+
 // make sure that validating using constructor really works
 threw = false;
 try {