Separate command history for sdb shell "ks"

[cyanpencil]

Closes #7649
Since I couldn't reuse RLineHistory, I added a simple list to RLine to keep last sdbshell commands.
I also check that a duplicate command is not inserted more than once (like dietline does)

[ret2libc]

I didn't really check, but... what about replacing core->cons->line with a new RLine (from r_line_new()) and using cmd_history_up and cmd_history_down?

[ret2libc]

Mmm, that's bad... most of the functions which work on RLine (e.g. r_line_history_add, etc.) use r_line_instance which is global...