in part for symmetry, and in part because it seems a good spot to add an indicator for the presence of a client certificate in the future.

It's been changed recently (see history & killed files) and I don't want to keep documenting it: users shouldn't mess with their history file that easily (this is not an excuse for sloppy parsing, which isn't the case.) Furthermore, the format is easy, I think intuitive, and the code easily found in fs.c.

The other option, less intrusive, would be to send the killed tabs in reverse order, but it'd seems strange when looking at the session file otherwise. So, add a `append' flag to kill_tab to optionally append the killed tab instead of pre-pending it.

free_tab now operates exclusively on the killed tabs list, so don't mention the current_tab.

when freeing a tab we have to release also its history.

Save closed tabs to a "killed tabs" queue, for up to a max of "max-killed-tabs", and allow to re-open them. Keep the tab history but not its content. This integrates nicely with the session file, just add the "killed" flag as alias for TAB_KILLED and put it in the ktabshead queue upon initalization. It's thus possible to re-open closed tabs even after telescope has been closed, and tabs keeps their history! Add a new cmd, cmd_tab_undo_close, to try to re-open the most recently closed tab and bind it to `u'. While here, add a TODO for the tab history memory leak.