core/vm, cmd/evm: standard vm traces

[cdetrio]

Some standardization (ethereum/tests#249) fixes for EVM traces.

[holiman]

I'm for these changes. They introduce one more if-debug block in the main interpreter loop, but I don't see quite how to get around that. If we want to optimize the evm, there are several other things we can do to shave off some time.

The main crux that this PR handles is that when the CALL gas is shaved down to 63/64 of the total gas, that operation is performed during the operation.gasCost(in.gasTable, in.evm, contract, stack, mem, memorySize) call. When this happens, the actual gas value on the stack is replaced . This PR thus makes a (shallow) copy of the stack (if debug is true), once every loop.

@fjl suggested that a better fix is to remove the swap-gas-stackitem-for-63/64 hack and instead use some callGas in the interpreter object, or somewhere.

That is probably a good idea, but I feel it's a bit too invasive at this point (with metro-changes to the evm already in progress) , and I don't feel comfortable doing that right now.

So I'm all for this patch. The standard vm traces are important for testing metro, and we've already found a post-metro consensus issue using fuzz testing.

[fjl]

I’m fine with this PR, but I doubt that the temporary hack will ever be removed.

[fjl]

Please use

 		// copies used by tracer
         stackCopy = newstack() // needed for Tracer since stack is mutated by 63/64 gas rule 
 		pcCopy    uint64       // needed for the deferred Tracer
 		gasCopy   uint64       // for Tracer to log gas remaining before execution
 		logged    bool         // deferred Tracer should ignore already logged steps

[cdetrio]

@fjl I made the requested changes.