[dist] add script to show differences between git and dist

diff-dist-git.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+
+set -e
+
+if [ ! -f "$1" ]; then
+	(
+		echo "Syntax: $0 [path-to-dist.tar.gz]"
+		echo
+		echo "Build such file with ./autogen.sh; ./configure; make dist-gzip"
+		echo "This tool can then be used to check the differences between the git"
+		echo "repository and the tar; it might show added files for autotools"
+		echo "(compile, configure, Makefile.in, m4, ...) and should remove"
+		echo ".gitignore files and some helper scripts (packdist.sh and this file)"
+	) >&2
+	exit 1
+fi
+
+tmpdir=$(mktemp --tmpdir -d diff-dist-tar-git-XXXXXXX)
+trap 'rm -rf "${tmpdir}"' EXIT
+
+git archive --format tar.gz -o "${tmpdir}/lighttpd.tar.gz" --prefix "lighttpd-2.0.0/" HEAD
+tardiff --modified --autoskip "${tmpdir}/lighttpd.tar.gz" "$1"