import: add --partial flag to create a changeset despite failed hunks The `hg import` command gains a `--partial` flag. When specified, a commit will always be created from a patch import. Any hunk that fails to apply will create .rej file, same as what `hg qimport` would do. This change is mainly aimed at preserving changeset metadata when applying a patch, something very important for reviewers. In case of failure with `--partial`, `hg import` returns 1 and the following message is displayed: patch applied partially (fix the .rej files and run `hg commit --amend`) When multiple patches are imported, we stop at the first one with failed hunks. In the future, someone may feel brave enough to tackle a --continue flag to import.