tests/test-debugrename.t

test: use a more verbose output in the test

While debugging some test failure, I released the test never checks if the
relevant changesets were preserved. So I am updating the test from `hg parents`
usage to `hg log -G` with a special template. This increase the area covered by
the test and clarify the test failures.

  $ hg init
  $ echo a > a
  $ hg ci -Am t
  adding a

  $ hg mv a b
  $ hg ci -Am t1
  $ hg debugrename b
  b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3

  $ hg mv b a
  $ hg ci -Am t2
  $ hg debugrename a
  a renamed from b:37d9b5d994eab34eda9c16b195ace52c7b129980

  $ hg debugrename --rev 1 b
  b renamed from a:b789fdd96dc2f3bd229c1dd8eedf0fc60e2b68e3