Backport core PRs to stable (#7892)

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

* 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

* parity-version pr reopen (#7136)

* parity-version module split from util

removed unused util deps and features

trigger buildbot again

only kvdb links rocksdb

snappy linker issues

* rm snappy

* fixed old version imports

* Move updater metadata to Cargo.toml of parity-version. (#7832)

* Update version.

* Bump parity version.

* Fix version.

* Fix compilation.

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,