title: checkout branch become checkout file
body: <p>Shell output:</p>
  
  <pre><code>Wener@Wener-PC /web/learn/angular/learn/angularjs-book
  $ git branch --l
  * forAnyOption
    forRawgithub
    master
    myMatser
  
  Wener@Wener-PC /web/learn/angular/learn/angularjs-book
  $ git co master
  切换到分支 'master'
  
  Wener@Wener-PC /web/learn/angular/learn/angularjs-book
  $ git co myMaster
  error: pathspec 'myMaster' did not match any file(s) known to git.
  
  Wener@Wener-PC /web/learn/angular/learn/angularjs-book
  $ git checkout myMaster
  error: pathspec 'myMaster' did not match any file(s) known to git.
  
  $ git --version
  git version 1.8.3.4
  </code></pre>
  
  <p>How to change branch directly ?</p>