Better full-screen frame support on MS-Windows.

Better full-screen frame support on MS-Windows.

 src/w32fns.c (w32_fullscreen_rect): New function to compute the
 window rectangle for the given fullscreen mode.
 (w32_wnd_proc): When in a fullscreen mode, WM_WINDOWPOSCHANGING no
 longer tunes the window size.  This keeps the window's edges flush
 with the screen and allows the taskbar to hide itself in fullboth.
 src/w32term.c (w32fullscreen_hook): 'fullboth' now shows without
 window decorations and uses the entire screen.
 src/w32term.h  (w32_fullscreen_rect) Add prototype.
 (struct w32_output): Replace normal_width, normal_height,
 normal_top, and normal_left members with a single normal_placement
 struct.
 (FRAME_NORMAL_WIDTH, FRAME_NORMAL_HEIGHT, FRAME_NORMAL_TOP):
 Remove macros.
 (FRAME_NORMAL_PLACEMENT): New macro.