IMPORT PATH MODIFICATION CHANGESET
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Please use this changeset as the first one on top of the original codebase.
Note that if there are new imports, they need to be changed as part of this
changeset. In general, use "git rebase" on github.com/jimmysong's version
and apply this changeset first.
Added more methods to blockchain.go

Restructured blockchain a little bit to help with common methods
Added tests for most of the errors