BCLV: Adjust arrow key behavior.

- Left/right arrow can now be used to collapse/expand the focus
  row. Holding shift reverts to the previous behavior of scrolling
  the view.

src/kits/interface/ColumnListView.cpp

@@ -1656,6 +1656,7 @@ BColumnListView::KeyDown(const char* bytes, int32 numBytes)
 		case B_RIGHT_ARROW:
 		case B_LEFT_ARROW:
 		{
+			if ((modifiers() & B_SHIFT_KEY) != 0) {
 				float  minVal, maxVal;
 				fHorizontalScrollBar->GetRange(&minVal, &maxVal);
 				float smallStep, largeStep;
@@ -1674,6 +1675,17 @@ BColumnListView::KeyDown(const char* bytes, int32 numBytes)
 					newVal = maxVal;
 
 				fHorizontalScrollBar->SetValue(newVal);
+			} else {
+				BRow* focusRow = fOutlineView->FocusRow();
+				if (focusRow == NULL)
+					break;
+
+				bool expanded = focusRow->IsExpanded();
+				if ((c == B_RIGHT_ARROW && !expanded)
+					|| (c == B_LEFT_ARROW && expanded)) {
+					fOutlineView->ToggleFocusRowOpen();
+				}
+			}
 			break;
 		}