title: fatal: git-write-tree: error building trees
body: <p>I did a <code>git pull</code> from a shared git repository, but something went really wrong, after I tried a <code>git revert</code>. Here is the situation now:</p>
  
  <pre><code>$ git stash
  Source/MediaStorageAndFileFormat/gdcmImageCodec.cxx: needs merge
  Source/MediaStorageAndFileFormat/gdcmJPEGLSCodec.cxx: needs merge
  Source/MediaStorageAndFileFormat/gdcmPNMCodec.cxx: needs merge
  Testing/Source/DataStructureAndEncodingDefinition/Cxx/TestDS.cxx: needs merge
  Utilities/socketxx/socket++/sockstream.cpp: needs merge
  Source/MediaStorageAndFileFormat/gdcmImageCodec.cxx: needs merge
  Source/MediaStorageAndFileFormat/gdcmJPEGLSCodec.cxx: needs merge
  Source/MediaStorageAndFileFormat/gdcmPNMCodec.cxx: needs merge
  Testing/Source/DataStructureAndEncodingDefinition/Cxx/TestDS.cxx: needs merge
  Utilities/socketxx/socket++/sockstream.cpp: needs merge
  Source/MediaStorageAndFileFormat/gdcmImageCodec.cxx: unmerged (2aafac967c35fa4e77c3086b83a3c102939ad168)
  Source/MediaStorageAndFileFormat/gdcmImageCodec.cxx: unmerged (78cc95e8bae85bf8345a7793676e878e83df167b)
  Source/MediaStorageAndFileFormat/gdcmImageCodec.cxx: unmerged (2524db713fbde0d7ebd86bfe2afc4b4d7d48db33)
  Source/MediaStorageAndFileFormat/gdcmJPEGLSCodec.cxx: unmerged (4bb4ba78973091eaa854b03c6ce24e8f4af9e7cc)
  Source/MediaStorageAndFileFormat/gdcmJPEGLSCodec.cxx: unmerged (ad0982b8b8b4c4fef23e69bbb639ca6d0cd98dd8)
  Source/MediaStorageAndFileFormat/gdcmJPEGLSCodec.cxx: unmerged (4868371b7218c6e007fb6c582ad4ab226167a80a)
  Source/MediaStorageAndFileFormat/gdcmPNMCodec.cxx: unmerged (f7a1b386b5b13b8fa8b6a31ce1258d2d5e5b13c5)
  Source/MediaStorageAndFileFormat/gdcmPNMCodec.cxx: unmerged (6ce299c416fbb3bb60e11ef1e54962ffd3449a4c)
  Source/MediaStorageAndFileFormat/gdcmPNMCodec.cxx: unmerged (75c8043a60a56a1130a34cdbd91d130bc9343c1c)
  Testing/Source/DataStructureAndEncodingDefinition/Cxx/TestDS.cxx: unmerged (79c2843f2649ea9c87fa57662dafd899a5fa39ee)
  ...
  fatal: git-write-tree: error building trees
  Cannot save the current index state
  </code></pre>
  
  <p>Is there a way to reset all that ?</p>
  
  <p>Thanks</p>