adding a DAV:namespace attribute for DAV:supported-xxx

John Vasta raised concerns about the difficulty of parsing
the DAV:name attribute for DAV:supported-live-property and
DAV:supported-report (because the DAV:name value might refer
to a namespace).  An XML-schema based parser would have
no trouble, but there are a bunch of non-XML-schema parsers
in use today (and probably will be for a while).

John also suggested a solution to this problem (what a guy!),
which is to have a DAV:namespace attribute (whose default
value is "DAV:") for those elements.

I think this is a good idea, and merits the generation of an
11.1 draft to capture it.  Any objections?

Cheers,
Geoff