Enable passing custom arguments to tmux

Custom arguments can now be passed to tmux by setting the
TMUXIFIER_TMUX_OPTS environment variable.

libexec/tmuxifier-current-session

@@ -14,7 +14,7 @@ Outputs the name of the current Tmux session."
 fi
 
 if [ -n "$TMUX" ]; then
-  for item in $(tmux list-pane -F "#{session_name}");do
+  for item in $(tmuxifier-tmux list-pane -F "#{session_name}");do
     echo $item
     exit 0
   done