Dear Maintainer,

When bootstrapping a new Debian packaging repository with gbp import-orig (and
by this I mean importing an orig tarball into an empty repository); an upstream
tarball containing a debian/ directory results in that directory being imported
into both the upstream and Debian packaging branches.

I think this is a sensible default. However, I don't see any straightforward
way to bootstrap a repository without upstream's debian/ directory being included
on the newly-created packaging branch while keeping upstream's debian/ directory
on the upstream branch.

For example, in an empty Git repository and a dummy upstream orig tarball:

    gbp import-orig \
        --debian-branch=master \
        --upstream-branch=upstream \
        --pristine-tar \
        --upstream-version=1.0.0 \
        ../dummy_v1.0.0.tar.gz


The debian/ directory from the orig tarball appears in both branches.