rendering_1: Extract READ-EVENT from HANDLE-ONE-EVENT.

  * A simple extract-method refactoring, not much to see here.
frame/application-frame: APPLICATION-FRAME protocol class and predicate.

  * This is a straightforward protocol class and predicate.
frame/application-frame-functions: Frames have a "pretty name".

  * The "pretty name" of a frame is, essentially, the window title.

  * No implementation yet, this is a file purely to hold the
generic function definitions.  And we're only adding the one pair
of functions for the moment (we'll add the rest over time, as we
find that we need them).
frame/standard-application-frame: Initial rough-in for the base frame class.

  * This is several things, and not much at all.  It establishes
the common superclass for most application frames.  It provides a
hook onto which we can hang some functionality.  And it consists
of a single slot with an accessor and an initarg.  It is the thin
end of the wedge for getting the frame, frame-manager, panes, top
level loop in place (basically the non-stream-based, non-gadget
parts of the application layer).
rendering_1,clx-interface: Use an APPLICATION-FRAME to pass the window title.

  * Instead of explicitly passing a window title, pass a frame
that has the title as its "pretty name".

  * Still going with the "thin end of the wedge" approach, as we
discard the frame immediately on both sides, but it gets an actual
frame instance involved in the interface, which is a start.