The subdirectory 'sub' is created early in the test file. Later, a test
case removes it during its clean-up actions. However, this test case is
protected by POSIXPERM. Consequently, 'sub' remains when the POSIXPERM
prerequisite is not satisfied. Later, a recently introduced test case
creates 'sub' again. Use -p with mkdir so that it does not fail if 'sub'
already exists.
Signed-off-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>