Downloads of multi-part uploaded files fail with s3cmd and the Java client

s3cmd and the Amazon AWS Java client (and potentially others) require that the ETag returned  for multi-part uploaded files contain a "-" character.  This requirement is not captured in the API spec, and appears to be a quirk implemented in these clients.  The issue was discovered as part of CloudStack development and testing (see http://mail-archives.apache.org/mod_mbox/cloudstack-dev/201306.mbox/%3C77B337AF224FD84CBF8401947098DD87038FCD%40SJCPEX01CL01.citrite.net%3E).

Thanks to Edison Su (@edisonsu) and Min Chen for running down the issue.