s3:lib add S-1-5-17 to well-known SID list

http://support.microsoft.com/kb/243330/en-us says the name is
"This organization", but Windows 2008 says IUSR

Picking the Windows 2008 variant as 'This Organization' would
be duplicate to S-1-5-15

source3/lib/util_wellknown.c

@@ -63,6 +63,7 @@ static const struct rid_name_map nt_authority_users[] = {
 	{ 13, "Terminal Server User"},
 	{ 14, "Remote Interactive Logon"},
 	{ 15, "This Organization"},
+	{ 17, "IUSR"},
 	{ 18, "SYSTEM"},
 	{ 19, "Local Service"},
 	{ 20, "Network Service"},