A reference can be found here:
<https://en.wikipedia.org/wiki/List_of_HTTP_status_codes>
(retrieved 2016-09-13).

Changes done:
Add set of 'HEAD method not available' before using fall back GET method.
Add new method in OPTIONS cache.
Add response status code if fall-back GET didn't succeeded.
Add copy-assignement operator to DAVOptions.
Fix behaviour of GET fall back when HEAD missing.

Change-Id: I6aad0e22bb444abf37b90186588f64f79b03cc3d
Reviewed-on: https://gerrit.libreoffice.org/29680Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Giuseppe Castagno <giuseppe.castagno@acca-esse.eu>