(Fset_window_hscroll, Fpos_visible_in_window_p):

(Fset_window_hscroll, Fpos_visible_in_window_p):
Doc fix.  Use "off-screen" instead of "invisible".
(Fwindow_line_height): Make line numbers 0-based.  Make line arg
optional; if nil, use current cursor row.  Handle text terminals
properly.  Return nil if non-interactive or pseudo-window.