Additional fix to #51 (eth_getCode on a non-contract should return 0x)

[HowardBraham]

Fixes #51

I don't think this issue was completely fixed before. In particular, the original comment was:

Not sure if this is an issue or not, but eth_getCode returns 0x0 for non-contract accounts. My assumption is that it should return 0x.

eth_getCode was still returning 0x0.

I deleted 3 lines from to.js, wrote 2 new test cases, and changed some old test cases from expecting 0x0 to expecting 0x.

Let me know if anything is wrong or missing.

[benjamincburns]

Thanks for contributing, @HowardBraham!