Comment 3 for bug 722726

Thanks for the report, and the patch. A couple of observations:

- The patch will be easier to review / apply if made from a VCS checkout of
  the sources in 'unidiff' format. See the following resources for help:

  http://docs.zope.org/developer/noncommitter-svn.html

  http://docs.zope.org/developer/noncommitter-bzr.html

- We need unit tests for any new feature added or bug fixed.

- In the tarfile case, we don't need to copy the file object into memory,
  because we can just hand the file handle to 'addfile'. To get the length,
  we should be using 'seek' and 'tell'.

- Likely the other export context types (directory, snapshot) should be
  reviewed to ensure they work equally well with the file object.