(struct scroll_bar): Rename member control_handle_low

(struct scroll_bar): Rename member control_handle_low
and control_handle_high to control_ref_low and control_ref_high.
All uses changed.
(SCROLL_BAR_CONTROL_REF, SET_SCROLL_BAR_CONTROL_REF): Rename from
SCROLL_BAR_CONTROL_HANDLE and SET_SCROLL_BAR_CONTROL_HANDLE,
respectively.  All uses changed.
(XCreatePixmap, XCreatePixmapFromBitmapData, XSetWindowBackground)
(install_window_handler, remove_window_handler): Replace WindowPtr
with WindowRef in externs.
(mac_get_window_bounds): Move extern from macfns.c.
(FRAME_OUTER_TO_INNER_DIFF_X, FRAME_OUTER_TO_INNER_DIFF_Y): New macros.
(struct mac_output) [USE_MAC_TOOLBAR]: New member toolbar_win_gravity.
(struct scroll_bar) [MAC_OSX]: New member fringe_extended_p.
(update_frame_tool_bar, free_frame_tool_bar) [USE_MAC_TOOLBAR]:
Add externs.