Make sendKeys and setValue send the whole string, not just characters

Looking at http://code.google.com/p/selenium/wiki/JsonWireProtocol#POST_/session/:sessionId/element/:id/value and http://code.google.com/p/selenium/wiki/JsonWireProtocol#POST_/session/:sessionId/keys the spec says the commands take an array of characters and should flatten them into a string before sending. What the code currently does is takes the first array element (which is a character). This doesn't seem to spec, and this patch fixes it.

I would imagine this is a client-breaking change (though I tested with my client) and I am new to the code so I'd like extra scrutiny on this

Fixed issue #12