Fix a bug where the root splitter's isvertical did not change if necessary...

Fix a bug where the root splitter's isvertical did not change if necessary when restoring a split pane. To repro:

1. Split vertically
2. Split horizontally

+---+---+
|   | B |
| A +---+
|   | C |
+---+---+

3. Close A
4. Undo close of A

The root splitter was  not reset to vertical after undo, so there were two horizontal splits.

sources/PTYTab.m

@@ -2406,6 +2406,7 @@ static void SetAgainstGrainDim(BOOL isVertical, NSSize *dest, CGFloat value) {
     while (root_.subviews.count) {
         [root_.subviews[0] removeFromSuperview];
     }
+    [root_ setVertical:tabToGut->root_.isVertical];
     while (tabToGut->root_.subviews.count) {
         [root_ addSubview:tabToGut->root_.subviews[0]];
     }