Take clonebundles into account

Currently, runner versions 0.2.x always perform a hg pull -r, even if the local repo has just been created.

This has the severe drawback of not leveraging clonebundles if there are any, making the first pull much slower and much more stressful for the server.

It's not hard, using hg debugcapabilities REMOTE_URL to detect that the remote repo has a clonebundle.