Some fixes for scroll bar code.

Some fixes for scroll bar code.

* w32term.c (w32_horizontal_scroll_bar_handle_click): In
`event->y' return entire range (the size of the scroll bar minus
that of the thumb).
* xterm.c (xm_scroll_callback, xaw_jump_callback): In `whole'
return entire range (the scaled size of the scroll bar minus
that of the slider).  In `portion' return the scaled position of
the slider.
(xaw_jump_callback): Restore part of code for vertical scroll
bar broken in change from 2014-07-27.
(xaw_scroll_callback): Provide incremental scrolling with
horizontal scroll bars.
(x_scroll_bar_handle_click): Fix typo introduced in change from
2014-07-27.
* scroll-bar.el (scroll-bar-horizontal-drag-1): Handle new
interpretation of `portion-whole'.