Fixes in window size functions around Bug#16430 and Bug#16470.

Fixes in window size functions around Bug#16430 and Bug#16470.

* window.c (Fwindow_pixel_width, Fwindow_pixel_height)
(Fwindow_mode_line_height, Fwindow_header_line_height)
(Fwindow_right_divider_width, Fwindow_bottom_divider_width):
Minor doc-string adjustments.
(Fwindow_total_height, Fwindow_total_width): New argument ROUND.
Rewrite doc-strings.
(window_body_height, window_body_width): Do not count partially
visible lines/columns when PIXELWISE is nil (Bug#16470).
(Qfloor, Qceiling): New symbols.
* window.el (window-total-size, window-size): New argument
ROUND.
(window--min-delta-1, window-min-delta, window--max-delta-1): Be
more conservative when calculating the numbers of lines or
columns a window can shrink (Bug#16430).
(fit-window-to-buffer): Simplify code.
* term.el (term-window-width): Call window-body-width again.