title: CMake: how to get subversion revision but not to fail if we made an export?
body: <p>I retrieve the subversion revision this way : </p>
  
  <pre><code>include(FindSubversion)
  IF(Subversion_FOUND) 
      Subversion_WC_INFO(${CMAKE_SOURCE_DIR} MY)
      SET(SVN_REVISION "${MY_WC_REVISION}")
  ELSE(Subversion_FOUND)
      SET(SVN_REVISION "-1")
  ENDIF(Subversion_FOUND) 
  </code></pre>
  
  <p>The problem is that when someone does "svn export" he can't compile : </p>
  
  <pre><code>-- Found Subversion: /usr/bin/svn (found version "1.6.11") 
  CMake Error at /opt/cmake-2.8.9-Linux-i386/share/cmake-2.8/Modules/FindSubversion.cmake:84 (MESSAGE):
    Command "/usr/bin/svn info /tmp/amore" failed with output:
  
    svn: '/tmp/amore' is not a working copy
  
  Call Stack (most recent call first):
    CMakeLists.txt:32 (Subversion_WC_INFO)
  </code></pre>
  
  <p>How to solve this problem in an elegant way ? </p>