Add x-remove-versions-location for feature: disable versioning

We can set x-versions-location empty to remove this header in API, but
to keep consistent, we should allow x-remove-versions-location too. The
usage is post "x-remove-versions-locaion: x", just like ACL remove
headers.

Fixed: bug #1107592

Change-Id: I1271eec6401d4a0e8c1a7c2d63aeb8dfef00bf6d
slobjects can not be made of other slobjects

Change-Id: Ib500f5fc2e890c3d23641350815a910168bcd543
Merge "Add x-remove-versions-location for feature: disable versioning"
Merge "slobjects can not be made of other slobjects"