Update Money to v5.1.1, to add rounding mode support
Remove BankersRoundingMoney, Money does this itself
Fix rounding alterations in the failing specs...

Since the Money update applies Bankers' Rounding by default, and also
because Ruby 1.9.2's built in version of BigDecimal had a bug when using
that rounding mode which caused it to wrongly round up some numbers, the
result of the premium schedule calculations has slightly changed.

Originally the default rounding mode in Money was Ruby's default (round
half up).