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For details, see previous commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

The branch object is managed by the sbinfo object as an element of its
internal array. The iinfo and dinfo objects contain the branch id, and
it will be used to implement the correct order in branch management
(add/del).

See also the documents in this commit.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>