[DAS2] DAS/2 writeback capability vs. writeable attribute

[Helt,Gregg]

In the current writeback spec, the ability of a server to support
writeback is indicated by: 
<CAPABILITY type="writeback" query_uri="..." /> 
under the versioned source element.
 
However, the retrieval spec talks about both the writeback capability
element and a "writeable" attribute for the versioned source element.  I
think the "writeable" attribute can be removed, since the capability
provides all the needed information.  The current writeback spec doesn't
mention this "writeable" element at all.
 
            gregg