refs #425 Log now has the step function name

Now the log messages have step function name if available.

```js
casper.start('http://www.foo.com/property/loginpage.php', function login() {
  this.fill('form', { username: 'abc', password: 'xyz'}, true);
});
```

then the log will look like

```
Step login (2/15) http://www.foo.com/property/loginpage.php (HTTP 200)
```

if the function is not named then it will look (note the extra spaces)

```
Step  (2/15) http://www.foo.com/property/loginpage.php (HTTP 200)
```