bookmark: complexity pull-push test to have deeper tree
This changeset only touch test.
The previous test was correct, it tested that the successors of an old bookmark
position was seen as a valid destination for bookmark.
However, a newer version is made for two reason:
(1) The new test check further. It check that the descendant of the successors
is a valid destination
(2) An ever more complexe test is needed to validate a future fix to issue 3680
Splitting complexification of the test and actual bugfix help to reduce the
noise in the bugfix changeset. Issue 3680 is NOT fixed by this changeset.
http://example.com/no/anchor, branches: (None, [])
http://example.com/an/anchor, branches: ('foo', [])
http://example.com/no/anchor/branches, branches: (None, ['foo'])
http://example.com/an/anchor/branches, branches: ('bar', ['foo'])
http://example.com/an/anchor/branches-None, branches: ('foo', [])
http://example.com/, branches: (None, [])
http://example.com/, branches: (None, [])
http://example.com/, branches: ('foo', [])