Added backward-compatible implementation for the `$element->value()` method that was introduced in selenium v2.42.0

See:

* https://code.google.com/p/selenium/source/browse/java/CHANGELOG
* https://code.google.com/p/selenium/source/detail?r=953007b48e83f90450f3e41b11ec31e2928f1605
Minor comment typo fix
Merge pull request #311 from zerkms/element-value-bc-selenium-2.42.0

Added backward-compatible implementation for the `$element->value()` method