Provide CLI options to disable aspects of soft-fork.

Soft-fork will remain default behaviour, but you can now disable
either the whole mechanism (you'll lose money if you mine with this
when the majority network doesn't) or just vote against it but
otherwise go with the flow.

json/src/spec/ethash.rs

@@ -42,6 +42,9 @@ pub struct EthashParams {
 	/// Homestead transition block number.
 	#[serde(rename="frontierCompatibilityModeLimit")]
 	pub frontier_compatibility_mode_limit: Uint,
+	/// DAO rescue soft-fork?
+	#[serde(rename="daoRescueSoftFork")]
+	pub dao_rescue_soft_fork: bool,
 }
 
 /// Ethash engine deserialization.
@@ -65,8 +68,9 @@ mod tests {
 				"difficultyBoundDivisor": "0x0800",
 				"durationLimit": "0x0d",
 				"blockReward": "0x4563918244F40000",
-				"registrar" : "0xc6d9d2cd449a754c494264e1809c50e34d64562b",
-				"frontierCompatibilityModeLimit" : "0x42"
+				"registrar": "0xc6d9d2cd449a754c494264e1809c50e34d64562b",
+				"frontierCompatibilityModeLimit": "0x42",
+				"daoRescueSoftFork": true
 			}
 		}"#;