store epoch transition proofs in DB

ethcore/src/migrations/state/v7.rs

@@ -238,7 +238,7 @@ impl Migration for OverlayRecentV7 {
 		}
 
 		let mut count = 0;
-		for (key, value) in source.iter(None) {
+		for (key, value) in source.iter(None).into_iter().flat_map(|inner| inner) {
 			count += 1;
 			if count == 100_000 {
 				count = 0;

ethcore/src/migrations/v10.rs

@@ -102,7 +102,7 @@ impl Migration for ToV10 {
 
 	fn migrate(&mut self, source: Arc<Database>, config: &Config, dest: &mut Database, col: Option<u32>) -> Result<(), Error> {
 		let mut batch = Batch::new(config, col);
-		for (key, value) in source.iter(col) {
+		for (key, value) in source.iter(col).into_iter().flat_map(|inner| inner) {
 			self.progress.tick();
 			batch.insert(key.to_vec(), value.to_vec(), dest)?;
 		}

ethcore/src/migrations/v9.rs

@@ -59,7 +59,7 @@ impl Migration for ToV9 {
 	fn migrate(&mut self, source: Arc<Database>, config: &Config, dest: &mut Database, col: Option<u32>) -> Result<(), Error> {
 		let mut batch = Batch::new(config, self.column);
 
-		for (key, value) in source.iter(col) {
+		for (key, value) in source.iter(col).into_iter().flat_map(|inner| inner) {
 			self.progress.tick();
 			match self.extract {
 				Extract::Header => {