WebDriverExpectedCondition::frameToBeAvailableAndSwitchToIt

According to [the original spec](http://selenium.googlecode.com/svn/trunk/docs/api/java/org/openqa/selenium/support/ui/ExpectedConditions.html) this is the only remaining missing expected condition.

I don't have a relevant testing environment, so I haven't put it through the ringer, but I figured I'd offer it up anyway.