title: project.vim reports "is not a valid directory" when refreshing or creating a project
body: <p>I'm using project.vim with VIm to manage large code bases with deep directory structures.</p>
  
  <p>When I switch to another one or create (\C) a new one and do a refresh (\R) project.vim starts displaying messages through the whole process for different directories:</p>
  
  <pre><code>&lt;dir_name&gt; is not a valid directory. [O]K:
  </code></pre>
  
  <p>I have to press Enter all the time, although the directories exist. I took a look at the code and it checks if the path is a directory. They are.
  Maybe there is a fix for this. The directories are under Perforce management, so everything is read-only.</p>
  
  <p>I have to stay at the keyboard and keep pressing Enter for it to go to next directories... For large code bases this is takes a long time.</p>
  
  <p>I contacted the author some time ago, but there was no response.</p>
  
  <p>Did anyone encounter this before?
  Could it be the it is bothered by the read-only-ness?
  Is there a fix for this? </p>
  
  <p>Thanks</p>