Verifying 100 new objects are fully connected to the existing DAG
is usually very cheap. Checking the entire Linux kernel history is
fully connected when pushing it to a new repository can take 30-60
seconds. Display a progress counter during this time so the client
knows the server is still working.
Change-Id: Iababe3ee1d35cb82f2bef2f12da7a2ecd03282b0