Geoff's prompt escape sequences patch (workers/23924)

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

I just noticed this never got committed to CVS.  I've tried it and it is
giving 99% of the correct behavior now (well, what I think is the correct
behavior; I never tried ending a prompt by turning ON standout, before).

The only glitch I can find by randomly fooling around is that completion
sometimes erases a standout space to the left of the word, inserts a plain
space, and then draws the completed word in standout, so you end up with
a command line with a "hole" in it.  Any further redraw of the line after
this point (such as completing again on a later word) repaints correctly
and fills the hole.

Fixing that probably means diving into the completion refresh code, so I
think committing what Geoff has so far would be fine.