repoview: use util.sha1() instead of hashlib.sha1() 45b5cd948a4d accidentally broke Python 2.4 compatibility, this fixes it.

debugobsolete: display parents information from markers Now that we have a new field, we need a way to visualize it.

obsmarkers: add a `parentnodes` method to retrieve parent information

obsstore: also store the 'parents' field on disk We now store the `parents` field on disk. We use the same strategy as for `date`: We stick it into the metadata. This is slow and dirty, but this is also the only way we currently have. At some point we'll have a new obsstore format to store this properly.

obsstore: drop 'date' from the metadata dictionary We are extracting the `date` information from the metadata at read time. However, we failed to remove it from the metadata returned in the markers. This is now fixed.

createmarkers: automatically record the parent of pruned changesets We need this information to build the set of relevant markers during exchanges. This can only be done at the `createmarkers` level since the `obsstore.create` function does not have a repo and therefore has no access to the parent information.