When deleting file, warn about deletion of its metadata

[onnozweers]

When you delete a file in dCache, all attached labels and extended attributes are lost. When you write a new version of the file with the same name, it will not have any of the labels and attributes of the previous version.

For a user, this may come as an unpleasant surprise. There might be valuable information in those attributes. For example: some labels might be needed to identify a file. When the label is lost, it might become very hard to find back the file by its identifier.

I do understand how this works in dCache: if you replace a file, for dCache it's the same as writing a completely new file, with a new internal ID.

But Ada can help. Ada could check, before deleting a file, whether it has any labels or extended attributes. If it has, Ada can throw an error. The user can then take measures not to lose the metadata. Ada should provide an option (--force or --including-metadata) to delete the file and all its metadata.

Thanks to Christine for reporting this.

[onnozweers]

For now, I've added a warning to the help text.
4a85d4f