The tmux-terminal-window command always spawns windows in the tmux
session where the Kakoune session was started - even if the calling
Kakoune client lives in a different tmux session.
Fix this by always creating the window in the tmux
session of the calling client. We already do the same for
tmux-terminal-{horizontal,vertical}.
I call tmux-terminal-impl with "new-window -a" (instead of
"new-window"), so make sure the fix works for my use case.
I considered retrieving the tmux session ID from the $TMUX environment
variable but the tmux manpage only specifies that $TMUX contains
"some internal data".
cfea884cf2