* Fix WebDAV by requesting new ETag conditionally
For me. this was saving only the first time and subsequently failing.
Having revised the requests, I noticed it didn't get a new ETag after saving.
Seems not all WebDAV implementations return a new ETag in PUT requests.
In my WebDAV service (WsgiDAV) - ETag is only served from a HEAD
request.
So if no ETag is found with PUT - we request one with HEAD.
This patch fixes error handling and should also work with servers that
provide ETag directly upon PUT.
* Add tweak from PMario
46e8e4343a