Fix memory leak in rollback (and more)

[sfan5]

• fix memory leak
• fix y2038 bug
• move to advanced settings, clarify description
• a few small code cleanups

[SmallJoker]

Looks good. Makes sense. Thank you.

As a possible improvement, we could consider to log a warning if sizeof(time_t) < 8.

[sfan5]

We could, but IMO it's the user's responsibility to know if their stdlib/libc is Y2038-compliant or not.

[appgurueu]

This is reasonable as-is 👍

p.s. another possible improvement: action_latest_buffer could profit from being turned into a std::deque.