t/t4004-diff-rename-symlink.sh: use three-arg <prereq>

t/t4004-diff-rename-symlink.sh: use three-arg <prereq>

Change the tests that skipped due to unavailable SYMLINKS support to
use the three-arg prereq form of test_expect_success.

This is like the "tests: implicitly skip SYMLINKS tests using
<prereq>" change, but I needed to create an additional test for some
setup code. It's in a separate change as suggested by Jonathan Nieder
for ease of reviewing.

    Date: Tue, 27 Jul 2010 16:17:37 -0500
    From: Jonathan Nieder <redacted>
    Message-ID: <redacted>
    In-Reply-To: <redacted>
    Subject: Re: [PATCH 1/4] tests: implicitly skip SYMLINKS tests using <prereq>

    Ævar Arnfjörð Bjarmason wrote:

    > +++ b/t/t4004-diff-rename-symlink.sh
    > @@ -40,8 +34,9 @@ test_expect_success \
    >  # rezrov and nitfol are rename/copy of frotz and bozbar should be
    >  # a new creation.
    >
    > -GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current
    > -cat >expected <<\EOF
    > +test_expect_success SYMLINKS 'setup diff output' "
    > +    GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current
    > +    cat >expected <<\EOF
    >  diff --git a/bozbar b/bozbar
    >  new file mode 120000
    >  --- /dev/null

    Probably belongs in a separate patch.  More importantly, it is missing
    &&-chaining (not a regression, but it is best to set a good example).

Reviewed-by: Jonathan Nieder <redacted>
Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
Signed-off-by: Junio C Hamano <redacted>