import: --obsolete flag for automatic obsolescence marker creation A new `--obsolete` flag is added to import. When present, the new node will be marked as a successors of the one specified in the `Node` field of the imported patch. No marker are created when revision have the node expected in the patch. This improves email based work flow where implicit rebase are likely to happen and extra information are lost, changing the hash. This new behavior requires a flags, otherwise the `hg export x | hg import -` idiom would change, turning the source obsolete. (Changing from `hg graft x` to `hg rebase --dest . --rev x`) This change only takes effect when using Mercurial 3.0 and above