Take account of fringe background extension in scroll_run_hook.
* w32term.c (w32_draw_fringe_bitmap): Rename local vars `left' and
`width' to `bar_area_x' and `bar_area_width', respectively.
(x_scroll_run): Take account of fringe background extension.
* xterm.c (x_draw_fringe_bitmap) [USE_TOOLKIT_SCROLL_BARS]: Rename
local vars `left' and `width' to `bar_area_x' and
`bar_area_width', respectively.
(x_scroll_run) [USE_TOOLKIT_SCROLL_BARS]: Take account of fringe
background extension.