Explicitly use "tip" in revision navigation.
Rationale: the tip revision is a moving target and if somebody wants tip,
it should be delivered.
adding dir/bar
adding foo
dir/bar
foo
adding dir/bar_2
adding foo_2
dir/bar_2
foo_2
adding a
adding c
adding b
adding d
removing a
removing c
recording removal of a as rename to b (100% similar)