Ensure that requesting version <= 0 doesn't
cause a runtime out of bounds dereference,
with a simple validation and accompanying tests
to ensure we never regress.
Since GetOp allows int64, it is fair game
that it should except out of range inputs,
plus this is an SDK so is bound to be abused
both unintentionally and intentionally.
Fixes#400
Refactor
* No more decorators, but rather types.AntiHandler
* No more handlers, but rather types.MsgHandler
* Ability to pass "stores" in NewXYZHandler()
* Coins live in types, and Accounts have coins
* Coinstore -> bank
* wip: tests and fixes for kvstore iteration
* update for latest tmlibs
* types compiles
* x/coin almost compiles
* x/coin: move things out of the way so it builds
* rebase fixes
* update glide
* add test for ChainDecorators
