Allow refund and tax/foodstamp/discount shift prefixes to appear
in any order. Technically, they can appear *anywhere* so all of
these would result in a tax-shifted, $1 refund to department 1:

RF1TN100DP10
1TNRF100DP10
1RF00D1TNP10

Obviously the last version is not preferred, but the preparser is
going to extract the refund and shift commands then knit together
whatever remains.