Fix select_window() by providing the session ID as argument to -t

Previosly select_window() would not work in nested tmux scenarios, as
there was no tmux session ID in the final tmux command. This is because
select_window() already adds the '-t' argument, hence the check in
cmd() does not add the session ID.

Thanks to Fabian Lesniak and Andreas Fried for pointing this out.

Fixes #161

Author: Flowdalic

libtmux/session.py

@@ -357,7 +357,10 @@ def select_window(self, target_window):
             assure ``-l``, ``-n``, ``-p`` work.
         """
 
-        target = '-t%s' % target_window
+        # Note that we also provide the session ID here, since cmd()
+        # will not automatically add it as there is already a '-t'
+        # argument provided.
+        target = '-t%s:%s' % (_session_id, target_window)
 
         proc = self.cmd('select-window', target)