filter-branch: Test renaming directories in a tree-filter
This test currently fails.
If b is a directory then 'mv a b' is not a plain "rename", but really a "move", so we must also test that the directory does not exist with the old name in the directory with the new name.
There's also some cleanup in the corresponding "rename file" test to avoid spurious shell syntax errors and "ambigous ref" error from 'git show' (but these should show up only if the test would fail anyway). Plus we also test for the non-existence of the old file.
Signed-off-by: Johannes Sixt <email@example.com>