Keypresses now go via content interface.
Contents don't shove the selection object into browser windows any more.
Contents report selection existence by sending message.
HTML content keeps track of where selections in it exist.
Contents report whether they have input focus via caret setting msg.
Caret can be hidden (can still input/paste) or removed.
Consolidate textarea selection handling.
Make textarea report its selection status changes to client.
Various textarea fixes.
Changed how we decide when to clear selections, and give focus.
