Backport Core PRs to beta (#7891)

* update back-references more aggressively after answering from cache (#7578)

* Add new EF ropstens nodes. (#7824)

* Add new EF ropstens nodes.

* Fix tests

* Add a timeout for light client sync requests (#7848)

* Add a timeout for light client sync requests

* Adjusting timeout to number of headers

* Flush keyfiles. Resolves #7632 (#7868)

* Fix wallet import (#7873)

* rpc: generate new account id for imported wallets

* ethstore: handle duplicate wallet filenames

* ethstore: simplify deduplication of wallet file names

* ethstore: do not dedup wallet filenames on update

* ethstore: fix minor grumbles

* [WASM] mem_cmp added to the Wasm runtime (#7539)

* mem_cmp added to the Wasm runtime

* schedule.wasm.mem_copy to schedule.wasm.mem_cmp for mem_cmp

* [Wasm] memcmp fix and test added (#7590)

* [Wasm] memcmp fix and test added

* [Wasm] use reqrep_test! macro for memcmp test

* wasmi interpreter (#7796)

* adjust storage update evm-style (#7812)

* disable internal memory (#7842)

ethcore/light/src/on_demand/mod.rs

@@ -90,7 +90,14 @@ impl Pending {
 			match self.requests[idx].respond_local(cache) {
 				Some(response) => {
 					self.requests.supply_response_unchecked(&response);
+
+					// update header and back-references after each from-cache
+					// response to ensure that the requests are left in a consistent
+					// state and increase the likelihood of being able to answer
+					// the next request from cache.
 					self.update_header_refs(idx, &response);
+					self.fill_unanswered();
+
 					self.responses.push(response);
 				}
 				None => break,