Change the tests that skipped due to unavailable SYMLINKS support to
use the three-arg prereq form of test_expect_success.
Now we get an indication of how many tests that need symlinks are
being skipped on platforms that don't support them.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>