title: CYGWIN=nodosfilewarning doesn't help cygwin warning
body: <p>When I try to use <code>ediff-revision</code> under Emacs 23.2.1 for a CVS-managed file, I receive the following error in the <code>*ediff-errors*</code> frame, instead of commencing directly to the ediff results:</p>
  
  <pre><code>cygwin warning:
    MS-DOS style path detected: c:/Users/BILL/AppData/Local/Temp/misc.cpp.~1.10~
    Preferred POSIX equivalent is: /cygdrive/c/Users/BILL/AppData/Local/Temp/misc.cpp.~1.10~
    CYGWIN environment variable option "nodosfilewarning" turns off this warning.
    Consult the user's guide for more details about POSIX paths:
      http://cygwin.com/cygwin-ug-net/using.html#using-pathnames
  </code></pre>
  
  <p>My problem is that I have already set that CYGWIN environment variable option "nodosfilewarning", so I have no idea why I am receiving this error.</p>
  
  <p>In fact, I can verify this right from an inferior shell under the same Emacs instance:</p>
  
  <pre><code>&gt; set | grep -i nodos
  CYGWIN=nodosfilewarning
  </code></pre>
  
  <p>I am running Cygwin 1.7.9-1 under Windows 7, in case this may be relevant (and I never had this problem before upgrading from Cygwin 1.5 to 1.7).</p>
  
  <p>Any idea how to get rid of this error?</p>
  
  <p>P.S. A subsequent call to <code>ediff-revision</code> succeeds without triggering this warning.</p>