(mac_display_info_for_display): Remove function.

(mac_display_info_for_display): Remove function.
(mac_flush_display_optional) [USE_CG_DRAWING]: New function.
(x_redisplay_interface) [USE_CG_DRAWING]: Set it as handler for
flush_display_optional.
[USE_TOOLKIT_SCROLL_BARS] (x_scroll_bar_handle_press): New
argument MOUSE_POS.  All uses changed.  Set bar->dragging to
negative integer if scroll bar handle is pressed.
[USE_TOOLKIT_SCROLL_BARS] (x_scroll_bar_handle_release): Negative
bar->dragging means scroll bar handle is not dragged.
[USE_TOOLKIT_SCROLL_BARS] (x_scroll_bar_handle_drag): Get initial
offset of scroll bar handle from negative bar->dragging.
(XTread_socket) [USE_TOOLKIT_SCROLL_BARS]: Modifiers for scroll
bar click is compared against mapped one.  Set down/up_modifier
for scroll bar click event with control key.