t/rebase: add failing tests for a peculiar revision

t/rebase: add failing tests for a peculiar revision

The following commands fail, even if :/quuxery and :/foomery resolve to
perfectly valid commits:

  $ git rebase [-i] --onto :/quuxery :/foomery

This is because rebase [-i] attempts to rev-parse ${REV}^0 to verify
that the given revision resolves to a commit.  Add tests to document
these failures.

Signed-off-by: Ramkumar Ramachandra <redacted>
Signed-off-by: Junio C Hamano <redacted>