Avoid relying on undefined behavior in assert.ObjectsAreEqual().

The previous assert.ObjectsAreEqual() implementation is broken in go 1.4beta1:

   x := uint64(3)
   log.Printf("equal? %t", assert.ObjectsAreEqual(3, x))

This prints "true" under Go 1.3 and "false" under 1.4beta1 (amd64/darwin).

The reason is that the ObjectsAreEqual() was comparing two reflect.Value values
for equality using ==, but the behavior of that operation is apparently
undefined (https://code.google.com/p/go/issues/detail?id=9034). The fix is to do
the type conversion and then do the comparison between two interface{} values.

assert/assertions.go

@@ -36,15 +36,13 @@ func ObjectsAreEqual(expected, actual interface{}) bool {
 		return true
 	}
 
-	expectedValue := reflect.ValueOf(expected)
-	actualValue := reflect.ValueOf(actual)
-	if expectedValue == actualValue {
-		return true
-	}
-
-	// Attempt comparison after type conversion
-	if actualValue.Type().ConvertibleTo(expectedValue.Type()) && expectedValue == actualValue.Convert(expectedValue.Type()) {
-		return true
+	actualType := reflect.TypeOf(actual)
+	if reflect.TypeOf(actual).ConvertibleTo(reflect.TypeOf(expected)) {
+		expectedValue := reflect.ValueOf(expected)
+		// Attempt comparison after type conversion
+		if actual == expectedValue.Convert(actualType).Interface() {
+			return true
+		}
 	}
 
 	// Last ditch effort