Select and Option no longer support ->value()

It looks like Selenium 2.42.0 has removed the support of the element/:id/value Command for some sorts of Elements like ```<select>``` and ```<option>```.
In the changelog for 2.42.0 I found only
>Removing outdated getValue command handler

This brakes the functionality of ```\PHPUnit_Extensions_Selenium2TestCase_Element_Select``` that uses the Options value for Methods like ```selectedValues```. They now only return an array containing a ```org.openqa.selenium.UnsupportedCommandException```.

This fix replaces all ->value() calls with ->attribute('value')