Further trackpad work:

When trackpad swipes don't convert to ScrollWheel steps anymore, several hardcoded
wheel events need to support swipe too.

This adds swipe support to:
- Menu item scroll
- Search item scroll
- ALT + number/slider/swatch values

The amount of old style scroll "clicks" is calculated based on how trackad is
being mapped to move a mouse pointer. Move it one widget unit = 1 click.

The swatch option applies trackpad swipe motion in analog way.

source/blender/editors/interface/interface_regions.c

@@ -896,8 +896,12 @@ void ui_searchbox_apply(uiBut *but, ARegion *ar)
 void ui_searchbox_event(bContext *C, ARegion *ar, uiBut *but, wmEvent *event)
 {
 	uiSearchboxData *data = ar->regiondata;
+	int type = event->type, val = event->val;
 	
-	switch (event->type) {
+	if (type == MOUSEPAN)
+		ui_pan_to_scroll(event, &type, &val);
+	
+	switch (type) {
 		case WHEELUPMOUSE:
 		case UPARROWKEY:
 			ui_searchbox_select(C, ar, but, -1);