Merge pull request #57 from dacoinminster/master

We already approved this awhile back under PR #46, but that one couldn't be merged automatically, so I created this one.
clarified tx 20 behavior
updated version to 0.4.5.1
Merge pull request #59 from marv-engine/sell_offer_fix

clarified tx 20 behavior re: available balance vs reserved, committed, escrowed
We've decided (in the dev mailing list) to not allow the buyer to purchase more btc than they reserved.

That is, overpayments are now simply lost bitcoins, rather than trying to write logic to determine if there are some unreserved coins for sale that the buyer could have in exchange for their overpayment.

Keeping it simple!