drag & drop of a parent tab to the bookmarks sidebar should (or shouldn't) handle only the parent tab not including children

[piroor]

On lately versions of TST, if you drag a parent of a tree to the bookmarks sidebar, then all of tabs in the tree are bookmarked instead of the parent one tab. In old versions, only the parent tab is bookmarked. People like the old behavior are confused by the new behavior. How to solve this problem?

1. Add a new secret preference to disable the new behavior.
2. Add a keyboard shortcut to disable the new behavior temporary.
3. Others.

One point. Now, the drag image for a dragging on a parent tab contains thumbnails of all tabs in the tree. If a drop make only one bookmark even if there are multiple thumbnails, it seems "unexpected result" from the feedback image...

[piroor]

I adopted the first plan.
6d3fd86
The configuration UI is not implemented yet.

[piroor]

UI is available now.
d4781a8