Backports into beta (#2512)

* RocksDB version bump

* Preserve cache on reverting the snapshot (#2488)

* Preserve cache on reverting the snapshot

* Renamed merge_with into replace_with

* Renamed and documented snapshotting methods

* Track dirty accounts in the state (#2461)

* State to track dirty accounts

* Removed clone_for_snapshot

* Renaming stuff

* Documentation and other minor fixes

* Replaced MaybeAccount with Option

* Adjustable stack size for EVM (#2483)

* stack size for io workers & evm threshold

* rust way to remember stack size

* right value

* 24kb size

* some stack reduction

* Fixed overflow panic in handshake_panic (#2495)

util/network/src/host.rs

@@ -580,7 +580,8 @@ impl Host {
 	}
 
 	fn handshake_count(&self) -> usize {
-		self.sessions.read().count() - self.session_count()
+		// session_count < total_count is possible because of the data race.
+		self.sessions.read().count().saturating_sub(self.session_count())
 	}
 
 	fn keep_alive(&self, io: &IoContext<NetworkIoMessage>) {