Proposal (WebDriverJS) - add a function to executeScript with a custom debugging msg

Not a fan of complicating the API like this.  I'm not quite sure what the best way to add this feature though. Some options:

 1. Leave `executeScript` as is and add `WebDriver.context` function. This would let you set a descriptive label to group commands:

        driver.context('log in', function() {
          driver.findElement(By.id('username')).sendKeys('bob');
          // ...
        });

 2. Use a fluent api to define reusable scripts(?)

        var script = driver.script("return arguments[0];").description("just do it");
        script.execute(1);  // or script.executeAsync