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)

ethcore/src/state_db.rs

@@ -190,7 +190,7 @@ impl StateDB {
 		for (address, account) in self.cache_overlay.drain(..) {
 			if let Some(&mut Some(ref mut existing)) = cache.accounts.get_mut(&address) {
 				if let Some(new) = account {
-					existing.merge_with(new);
+					existing.overwrite_with(new);
 					continue;
 				}
 			}