title: git-p4 clone command fails
body: <p>I'm trying to run this command: git-p4 clone -v //depot/path/project/v31a</p>
  
  <p>And it fails with error:</p>
  
  <p>Importing from //depot/path/project into project</p>
  
  <p>Reinitialized existing Git repository in /home/xxx/Downloads/p4tmp/v31a/.git/</p>
  
  <p>Reading pipe: ['git', 'config', '--bool', 'git-p4.useclientspec']</p>
  
  <p>Doing initial import of //depot/path/project/v31a/ from revision #head into refs/remotes/p4/master</p>
  
  <p>Reading pipe: ['git', 'config', 'git-p4.user']</p>
  
  <p>Reading pipe: ['git', 'config', 'git-p4.password']</p>
  
  <p>Reading pipe: ['git', 'config', 'git-p4.port']</p>
  
  <p>Reading pipe: ['git', 'config', 'git-p4.host']</p>
  
  <p>Reading pipe: ['git', 'config', 'git-p4.client']</p>
  
  <p>Opening pipe: ['p4', '-G', 'files', '//depot/path/project/v31a/...#head']</p>
  
  <p>Opening pipe: ['p4', '-G', 'describe', '-s', '222342']</p>
  
  <p>Reading pipe: ['git', 'config', '--bool', 'core.ignorecase']</p>
  
  <p>commit into refs/remotes/p4/master</p>
  
  <p>Opening pipe: p4 -G users</p>
  
  <p><strong>IO error with git fast-import. Is your git version recent enough?</strong></p>
  
  <p>==============================================</p>
  
  <p>Before this, I have set P4HOST, P4USER AND P4PASSWD environment variables.</p>
  
  <p>Any idea what this error is? My git version is 2.3.6.</p>