Enhancement: Add Apple Keyboard Dock Support (or "Enter" Key support)

[garoffoli]

As of prerelease-6 (the latest that will work on the iPad 1, running iOS 5.1.1), sending a message requires the user to press the "Send" button to send a message.
But if a user uses a keyboard (Bluetooth or Dock) he has to write the message on the keyboard and the click the screen to send it, and quickly it becomes annoying. The fix is to enable the text field to enable the "Enter" key on the keyboard to send the message