edits on BIND draft

On

<http://greenbytes.de/tech/webdav/draft-ietf-webdav-bind-latest.html>:

- Add issues "ED_authors" and "ED_updates".
- Add section about capability discovery (DAV header).
- Close issue "5.1_LOOP_STATUS" (only use 208 status when client signals 
  support for the BIND spec).

Feedback appreciated,

Julian

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