[PATCH v2 0/5] Skip tests using 3-arg test_*

This is just like v1 aside from:
    
    diff --git a/t/t4004-diff-rename-symlink.sh b/t/t4004-diff-rename-symlink.sh
    index 85a77b3..92a65f4 100755
    --- a/t/t4004-diff-rename-symlink.sh
    +++ b/t/t4004-diff-rename-symlink.sh
    @@ -38 +38 @@ test_expect_success SYMLINKS 'setup diff output' "
    -    GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current
    +    GIT_DIFF_OPTS=--unified=0 git diff-index -M -p $tree >current &&

But I also split the change I made to t/t4004-diff-rename-symlink.sh from the "tests: implicitly skip SYMLINKS tests using <prereq>" patch as suggested by Jonathan Nieder.

It was the only one in the aforementioned commit that didn't just nuke
skip_all=* + do 's/success /success SYMLINKS /', so it deserved a
separate patch.
    
Ævar Arnfjörð Bjarmason (5):
  tests: implicitly skip SYMLINKS tests using <prereq>
  t/t4004-diff-rename-symlink.sh: use three-arg <prereq>
  t/t5800-remote-helpers.sh: Skip with prereq on python <2.4
  t/t7800-difftool.sh: Skip with prereq on no PERL
  t/README: Update "Skipping tests" to align with best practices

 t/README                          |   21 +++++++++++++--
 t/t2007-checkout-symlink.sh       |   14 +++-------
 t/t4004-diff-rename-symlink.sh    |   18 +++++--------
 t/t4011-diff-symlink.sh           |   18 ++++---------
 t/t4023-diff-rename-typechange.sh |   14 +++-------
 t/t4114-apply-typechange.sh       |   28 ++++++++-------------
 t/t4115-apply-symlink.sh          |   12 ++-------
 t/t4122-apply-symlink-inside.sh   |   12 ++-------
 t/t5522-pull-symlink.sh           |   14 +++-------
 t/t5800-remote-helpers.sh         |   24 ++++++++----------
 t/t6035-merge-dir-to-symlink.sh   |   20 +++++----------
 t/t7800-difftool.sh               |   49 ++++++++++++++++--------------------
 12 files changed, 100 insertions(+), 144 deletions(-)