config: explicitly track the use of the standard default value We introduce a small object used to detect that no specific default value has been passed to 'ui.config'. We need this explicit special value since "None" is a valid and common default value. The end goal here is to make progress on a centralised and explicit declaration of the available config option. A first good usecase for this are "default" value. Before starting looking further down this alley we needs to rework the handling of default value in the 'ui' object to have all configxyz methods going through the same logic. This is the first changeset on this trek.

clonebundle: update hook arguments (BC) By calling applybundle() with 'clonebundles' and the url instead of calling processbundle(), the hooks will get different arguments: HG_SOURCE will be 'clonebundles' instead of 'bundle2' and HG_URL will be the url instead of 'bundle2'. This is consistent with the bundle1 behavior and seems like a bug fix, but I'm marking it BC anyway.