* [DEV-149] Add test case for CVE-2018-17144 (Bitcoin DoS/Double Spend bug)
* [DEV-149] change t.Errorf + return to t.Fatalf
* [DEV-149] fix malformed blocks
* [DEV-149] change test blocks to use simnet genesis
* [DEV-92] Covered lookupPreviousNodes in tests.
* [DEV-92] Covered accept.go in tests.
* [DEV-92] Fixed a typo.
* [DEV-92] Covered blockindex.go in tests.
* [DEV-92] Replaced Errorf + return with Errorf. Added the test case to the error messages.
* [DEV-92] Fixed grammar in a comment.
* [DEV-92] Split casting error checking and ErrorCode checking into separate tests.
* [DEV-92] Improved errors.
* [DEV-92] Made errors a tiny bit more descriptive.