title: SVN upgrade fails
body: <p>When I tried to update my working SVN copy, I got the following error message,</p>
  
  <pre><code>svn: E155036: Please see the 'svn upgrade' command
  svn: E155036: Working copy '/path/to/repository' is too old (format 10, created by Subversion 1.6)
  </code></pre>
  
  <p>So I tried to execute the 'svn upgrade' command.
  At first everything seems to be working, for every file in working copy I get the following message,</p>
  
  <pre><code>Upgraded 'path/to/file'
  </code></pre>
  
  <p>After the process is finished with looping over my working copy files I get the following error message,</p>
  
  <pre><code>enter svn: E235000: In file '/SourceCache/subversion/subversion-62/subversion/subversion/libsvn_wc/entries.c' line 1713: assertion failed (base_node || below_working_node)
  Abort trap: 6
  </code></pre>
  
  <p>I work on a Mac OS X 10.9 machine with SVN 1.7.</p>
  
  <p>Can anyone help me?</p>
  
  <p>Thanks in advance.</p>