Document pixelwise frame resizing and fix related bug on Windows.

Document pixelwise frame resizing and fix related bug on Windows.

* w32term.c (x_set_window_size): When frame-resize-pixelwise is
nil, always resize character wise to avoid potential loss of the
mode line (Bug#16923 related).
* display.texi (Temporary Displays): Say that
with-temp-buffer-window makes its buffer current.
* frames.texi (Size and Position): Describe new option
`frame-resize-pixelwise'.  Rewrite descriptions of
`set-frame-size', `set-frame-height' and `set-frame-width'.