When responding to '#', the Qt interface puts up a grid of buttons
labelled with the names of commands. Then if the user types
instead of clicking on a button, buttons which can no longer match
are removed rather than grayed out. The remaining ones keep their
same relative positions. Once whole rows or whole columns were
gone, it looked awful. With rows gone, the size of the grid
shrank but the popup stayed the same size, so the one-line prompt
area expanded to fill up the vacated vertical space. That caused
the prompt and partial response to move as they stayed centered in
their growing area. With columns gone, the width of the buttons
in remaining columns expanded and they spread out to take up
vacated horizontal space. Once the candidate commands were all
in one column, the buttons spanned the width of the grid. (That's
mostly my fault due to changing the grid from being row-oriented
[a b c]
[d e ]
to column oriented
[a d]
[b e]
[c ]
which resulted in columns going away a lot faster and possibly down
to one when the old layout always had at least two. But old layout
could drop to one row; the current layout always has at least two.)
Also, accept ^[ as ESC. Typing ESC when partial input is present
kills that input but keeps prompting. Typing ESC when no input
is present (none entered yet or a second of two consecutive ESCs)
cancels the operation.
Allow ^U to kill partial input. If used when no input is present,
nothing happens, similar to backspace. Unlike tty and curses, it's
hardcoded here. That shouldn't be a problem because ESC can be
used as a substitute if ^U isn't what the player normally uses.
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