Incoming changes in the sh(1) default behaviour

[Baptiste Daroussin]

Hello everyone

We have been working implementing the persistent history storage in sh(1).

It will now respect POSIX:
- by default the history will be saved and loaded from ~/.sh_history
- if HISTFILE is set it will use histfile instead of ~/.sh_history
- if HISTFILE is set but empty it will not load or save anything
- if HISTSIZE is set to 0 it will also not load or save anything

The change will be pushed very soon to head and probably not be MFC except if
someone manage to convince me otherwise.

https://reviews.freebsd.org/D29493

Best regards,
Bapt