Session Save / Restore.
The old session code saved the sessions in random order, the restore
order was wrong and it ignored the splits (even the old style splits
where ignored, I'm not talking about the new style). This new session
/ restore code ignores nothing: It will save and restore your whole
Terminal Hierarchy, with splits, splits-in-splits, recursing everything
bug: unfocused terminal tabs lacks title untill focused. should be
easy to fix and not a blocker.