Issue 482: PropFind::set() hard adds properties during ALLPROPS

See Issue 482. Properties handled on propFind with PropFind::set() were
not being added to an ALLPROPS response, even though that would be
expected. Ensure that any properties being added through set() are added
to an ALLPROPS response.
Merge pull request #486 from aklomp/issue482

Issue #482: PropFind::set() hard adds properties during ALLPROPS