title: Making files read-only until checked out
body: <p>I need to make the project files read-only by default, and make them writable if and only if I check out the files for local editing.</p>
  
  <p>I thought that was the default behavior, but for some reason I lost it. How could I get it back?</p>
  
  <p>(My ultimate intention is to prevent developers from editing files without first checking out.)</p>