title: vimrc: how to auto change window focus when vim is loaded
body: <p>I've let tagbar and NERDtree autoload when vim is opening any file. 
     The window layout from left to right is:</p>
  
  <blockquote>
    <p>NERDTree----My source code----TagBar</p>
  </blockquote>
  
  <p>The problem is, each time vim is up, the NERDtree on the left gets the focus(keyboard). I wish to make the middle window(My source code) having the focus, so I can start coding immediately. Or else I have to C-w l to switch windows each time.</p>
  
  <p>How to set this in ~/.vimrc?</p>
  
  <p>Thanks a lot.</p>