Folder: Ignore change from the watcher if the file has not changed its mtime or size...

Folder: Ignore change from the watcher if the file has not changed its mtime or size (#4942)

For issue #4927:
On Windows 10, we get a notification after the sync is finished for file that were
just downloaded. The guard we have against our "own changes" are only working when
the sync is running and the OwncloudPropagator still alive.