Make SlimuxSendKeysLast send last prompted-for keys instead of last sent keys

[slashfoo]

SlimuxSendKeysLast prompts if one hasn't specified what to send, and then keeps sending that.

When someone uses SlimuxSendKeys command to send keys, however, the last sent gets overwritten and one would need to re-enter what was typed at the prompt.

I think separating the last-sent from the path by SlimuxSendKeys, and only involve the *Prompt and *Last commands it would avoid this problem.