Fix session phase in early-exit (#453)

* Fix up session phase.

* Version bump

* Fix session rotation properly and add test

* Update runtimes

* Docs

polkadot/runtime/src/lib.rs

@@ -110,7 +110,7 @@ pub const VERSION: RuntimeVersion = RuntimeVersion {
 	spec_name: ver_str!("polkadot"),
 	impl_name: ver_str!("parity-polkadot"),
 	authoring_version: 1,
-	spec_version: 2,
+	spec_version: 100,
 	impl_version: 0,
 };