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.