Switch from SHARE_HISTORY to INC_APPEND_HISTORY.

Dave was complaining about SHARE history, because he usually wants to
know what he's done in /this/ shell lately, not any shell. After
considering it for a while, I think I agree.

INC_APPEND_HISTORY is kind of the best of both. History of the current
shell takes precedence, but when opening a new shell, all past history
is shared in chronological order.
Add a random handful of history options.

Just new features I found out about and I thought I would enable.