Discovery: consider also the "shared by me" as shared

The "S" in the permission is only for the "Shared with me" files.
It is only used to show the shared status in the overlay icons.
But we also wish to show the shared status for files that are shared
"by" the users. We can find that out using the 'share-types' webdav
property. If set, then we are sharing the object.
We fake a 'S' in the permission as for our purpose, they mean the same.

Issue #4788