Add a RefFilter interface to ReceivePack and UploadPack

When a user of ReceivePack or UploadPack wants to control what refs
are sent to the client, for instance when some refs should be hidden
from some clients, this interface can be extended to provide a fine
grained control over what refs are sent to the client.

Change-Id: Ie6320b0f8922e1a5e1bad91c016bd476ea094366
3 files changed