* ECIP 1041 - Remove Difficulty Bomb (#7905)
Enable difficulty bomb defusion at block:
- 5900000 on Ethereum Classic mainnet,
- 2300000 on morden testnet.
Reference:
https://github.com/ethereumproject/ECIPs/blob/master/ECIPs/ECIP-1041.md
* spec: Validate required divisor fields are not 0 (#7933)
* Add validate_non_zero function
It's used to validate that a Spec's uint field used as a divisor is not zero.
* Add deserialize_with to gas_limit_bound_divisor
Prevents panics due to divide-by-zero on the gas_limit_bound_divisor
field.
* Add deserialize_with to difficulty_bound_divisor
Prevents panics due to divide-by-zero on the difficulty_bound_divisor
field.
* Add validate_optional_non_zero function
Used to validate Option<Uint> divisor fields.
* Use deserialize_with on optional divisor fields.
* Add #[serde(default)] attribute to divisor fields
When using `#[serde(deserialize_with)]`, `#[serde(default)]` must be specified so that missing
fields can be deserialized with the deserializer for `None`.
* Kovan WASM fork code (#7849)
* kovan fork code
* introduce ethcore level vm_factory and let it fail
* fix json tests
* wasmcosts as option
* review changes
* wasm costs in parser
* fix evm tests
* review fixes
* fix test
* remove redundant json field
