Set WINDOW's buffer to BUFFER.
WINDOW must be a live window and defaults to the selected one.
Optional argument START non-nil means set WINDOW's start position
to START. Optional argument POINT non-nil means set WINDOW's
point to POINT. If WINDOW is selected this also sets BUFFER's
`point' to POINT. If WINDOW is selected and the buffer it showed
before was current this also makes BUFFER the current buffer.