There are several different object types in a versioned table,
which will determine the exact behaviour.
The object type states are:
* Pending - the object is yet to be committed and is being uploaded.
* Committed - the object has been finished and can be read.
* DeleteMarker - indicates that the object should be treated as not
present when is at the top of the version stack.
There are also versioning states:
* Unversioned - only one unversioned object is allowed per object key.
* Versioned - multiple objects with the same key are allowed.
Change-Id: I65dfa781e8da253a4e5d572b799d53c351196eee
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