Bug in SLO with multipart-manifest=get content type.

In trying to override the content-type for the convenience
call I broke COPYs and POSTs for SLO. yaaa...

Change-Id: Ifbcda6d2dd0ee43e43d62e58a90301e7afd05e27
Merge "Bug in SLO with multipart-manifest=get content type."