Set the REPL window title using xdotool

As mentioned in issue #2973, the -t argument for setting the terminal
title was not very portable.

rc/windowing/repl/x11.kak

@@ -15,7 +15,9 @@ All optional parameters are forwarded to the new window} \
            exit
         fi
         if [ $# -eq 0 ]; then cmd="${SHELL:-sh}"; else cmd="$@"; fi
-        setsid ${kak_opt_termcmd} ${cmd} -t kak_repl_window < /dev/null > /dev/null 2>&1 &
+        setsid ${kak_opt_termcmd} \
+               "xdotool getactivewindow set_window --name kak_repl_window \
+                && exec \"${cmd}\"" < /dev/null > /dev/null 2>&1 &
 }}
 
 define-command x11-send-text -docstring "send the selected text to the repl window" %{