Ethereum classic (#1706)

* Add Ethereum Classic support

(Rename homestead-dogmatic -> classic)

* Additional change needed.

* More needed changes.

* Separate database path for known forks.

* Address minor grumble.

json/src/spec/spec.rs

@@ -26,6 +26,9 @@ use spec::{Params, Genesis, Engine, State};
 pub struct Spec {
 	/// Spec name.
 	pub name: String,
+	/// Special fork name.
+	#[serde(rename="forkName")]
+	pub fork_name: Option<String>,
 	/// Engine.
 	pub engine: Engine,
 	/// Spec params.