specify explicit "--pretty=medium" with `git log/show/whatchanged`

The following patch will introduce a new configuration variable,
"format.pretty", from then on the pretty format without specifying
"--pretty" might not be the default "--pretty=medium", it depends on
the user's config. So all kinds of Shell/Perl/Emacs scripts that needs
the default medium pretty format must specify it explicitly.

Signed-off-by: Denis Cheng <crquan@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/git-cvsserver.perl b/git-cvsserver.perl
index afe3d0b..7f632af 100755
--- a/git-cvsserver.perl
+++ b/git-cvsserver.perl
@@ -2556,7 +2556,7 @@
                     if ($base) {
                         my @merged;
                         # print "want to log between  $base $parent \n";
-                        open(GITLOG, '-|', 'git-log', "$base..$parent")
+                        open(GITLOG, '-|', 'git-log', '--pretty=medium', "$base..$parent")
 			  or die "Cannot call git-log: $!";
                         my $mergedhash;
                         while (<GITLOG>) {