Add a regression test for kern/21768.

MFC after:	1 week

tools/regression/vfs/trailing_slash.t

@@ -0,0 +1,42 @@
+#!/bin/sh
+#
+# $FreeBSD$
+#
+# Tests vfs_lookup()'s handling of trailing slashes for symlinks that
+# point to files.  See kern/21768
+#
+
+testfile="/tmp/testfile-$$"
+testlink="/tmp/testlink-$$"
+
+tests="
+$testfile:$testlink:$testfile:0
+$testfile:$testlink:$testfile/:1
+$testfile:$testlink:$testlink:0
+$testfile:$testlink:$testlink/:1
+$testfile/:$testlink:$testlink:1
+$testfile/:$testlink:$testlink/:1
+"
+
+touch $testfile || exit 1
+trap "rm $testfile $testlink" EXIT
+
+set $tests
+echo "1..$#"
+n=1
+for testspec ; do
+	(
+		IFS=:
+		set $testspec
+		unset IFS
+		ln -fs "$1" "$2" || exit 1
+		cat "$3" >/dev/null 2>&1
+		ret=$?
+		if [ "$ret" -eq "$4" ] ; then
+			echo "ok $n"
+		else
+			echo "fail $n - expected $4, got $ret"
+		fi
+		n=$((n+1))
+	)
+done