Adding a prebuilt copy of the SafariDriver and embedding it in the java client jar.
This prebuilt will be automatically unpacked and installed when creating a new
SafariDriver instance. To use a custom version of the SafariDriver, set the
webdriver.safari.driver system property:
  java -jar selenium.jar -Dwebdriver.safari.driver=/custom/SafariDriver.safariextz

To disable installing the extension on start-up and use an existing version, use
the webdriver.safari.noinstall system property:
  java -jar selenium.jar -Dwebdriver.safari.noinstall=true

Fixes issue 4107