Fancy tracer mhs

[holiman]

Adds blocknumber, gaslimit to ctx, adds db to result, and implements three tracers:

• 4bytes.js returns info about ABI calldata (signature and argument length)
• prestate.js generates a geth genesis from a transaction, for local replay
• tracefunc.js returns data suitable for evmdis disassembly, to get intelligent traces. Original version by @Arachnid

[karalabe]

A nicer approach imho would be to add this once to ctx. I.e. place something like this at the top of this function:

if pc == 0 {
	jst.ctx["block"] = env.BlockNumber.Uint64()
}

Also please note, the gasLimit is already part of the context and it's called gas.

[karalabe]

If pc can be 0 multiple times (unsure how subcalls work with regard to pc), we can add an inited bool field to jst which will be set to true when entering this method for the first time so we only set the block number once.

[holiman]

Hmm... though, I did mean block gas limit, but transaction gas limit works aswell in my particular usecase.

Yes, pc can be 0 multiple times

[holiman]

(even without subcalls, since the first opcode can be jumpdest)

[karalabe]

I've cherry picked these commits to fix some minor things.