1) Add support for ordinary terminals by using the curses library.

1) Add support for ordinary terminals by using the curses library.

2) Eliminate some interrupt windows in direct output.

3) Add operations to the screen data structure to accomodate curses.

4) Add a new structure, a display, which consists of a keyboard and a screen.

5) Conditions not trapped by edwin now revert to the user in a
reasonable way, ie. the terminal should be in the same state that it
was before edwin was entered.

6) Reentering edwin after an unhandled condition updates the display.

7) The interaction buffer prompt is now inserted in the "exit" thunk
of the dynamic unwind, so that an abort will insert it as well.

8) Fix wrong number of args bug in ^R Screen Video.