Set WINDOW's previous buffers to PREV-BUFFERS.
WINDOW must be a live window and defaults to the selected one.
PREV-BUFFERS should be a list of elements (BUFFER WINDOW-START POS),
where BUFFER is a buffer, WINDOW-START is the start position of the
window for that buffer, and POS is a window-specific point value.
(fn WINDOW PREV-BUFFERS)