filter-branch: add example to move everything into a subdirectory

This is based on Jeff King's example in

	20070621130137.GB4487@coredump.intra.peff.net
Signed-off-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-filter-branch.sh

@@ -178,6 +178,14 @@
 #
 #	git-filter-branch ... new-H C..H --not D
 #	git-filter-branch ... new-H D..H --not C
+#
+# To move the whole tree into a subdirectory, or remove it from there:
+#
+# git-filter-branch --index-filter \
+#	'git-ls-files -s | sed "s-\t-&newsubdir/-" |
+#		GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
+#			git-update-index --index-info &&
+#	 mv $GIT_INDEX_FILE.new $GIT_INDEX_FILE' directorymoved
 
 # Testsuite: TODO
 

t/t7003-filter-branch.sh

@@ -99,4 +99,12 @@ test_expect_success 'subdirectory filter result looks okay' '
 	! git show sub:subdir
 '
 
+test_expect_success 'use index-filter to move into a subdirectory' '
+	git-filter-branch --index-filter \
+		 "git-ls-files -s | sed \"s-\\t-&newsubdir/-\" |
+	          GIT_INDEX_FILE=\$GIT_INDEX_FILE.new \
+			git-update-index --index-info &&
+		  mv \$GIT_INDEX_FILE.new \$GIT_INDEX_FILE" directorymoved &&
+	test -z "$(git diff HEAD directorymoved:newsubdir)"'
+
 test_done