Previously, it would keep the old buffer displayed why typing over
it. I had kept it thus because I didn't want to erase the buffer
right away because the behavior is that when we type nothing, we
keep the buffer as-is and repeat the action.
Now, the behavior of I and F is much better. It keeps the buffer
displayed until the first non-return keystroke and then erases it.
Also, fixed PSP leak in _type and fixed PSP overuse in successful
_F (they balanced out).
Also, add insert and find buffers to the header, making it 3 lines
high.
Also, fix the "I" overshadowing word which wasn't operating on the
proper RSP level.
Also, fix I which didn't mark the block as dirty.
Also, made LIST properly handle full 64-chars lines not ending with
a null or CR. Previously, such a line would be accompanied by its
following line, duplicating that line's output.
