Implement an interoperability test for fetch-pack/upload-pack

The next patches will extend the pack protocol. This test assures that this
extension is compatible to earlier versions of git-fetch-pack/git-upload-pack.

All you need to do to take advantage of this test, is to install older
known-to-be-working binaries in the path as "old-git-fetch-pack" and
"old-git-upload-pack".

Note that the warning when testing with old-git-fetch-pack is to be
expected (it just says that the old version was not taking advantage
of all the information which the server sent).

Signed-off-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>

t/t5501-old-fetch-and-upload.sh

@@ -0,0 +1,43 @@
+#!/bin/sh
+#
+# Copyright (c) 2005 Johannes Schindelin
+#
+
+# Test that the current fetch-pack/upload-pack plays nicely with
+# an old counterpart
+
+cd $(dirname $0) || exit 1
+
+tmp=$(mktemp tmp-XXXX)
+
+retval=0
+
+if [ -z "$1" ]; then
+	list="fetch upload"
+else
+	list="$@"
+fi
+
+for i in $list; do
+	case "$i" in
+	fetch) pgm="old-git-fetch-pack"; replace="$pgm";;
+	upload) pgm="old-git-upload-pack"; replace="git-fetch-pack --exec=$pgm";;
+	both) pgm="old-git-upload-pack"; replace="old-git-fetch-pack --exec=$pgm";;
+	esac
+
+	if which $pgm; then
+		echo "Testing with $pgm"
+		sed -e "s/git-fetch-pack/$replace/g" \
+			-e "s/# old fails/warn/" < t5500-fetch-pack.sh > $tmp
+
+		sh $tmp || retval=$?
+		rm $tmp
+
+		test $retval != 0 && exit $retval
+	else
+		echo "Skipping test for $i, since I cannot find $pgm"
+	fi
+done
+
+exit 0
+