Merge branch 'master' into dp/make-CallExecutors-generic-over-hasher-and-rlpcodec

* master:
  Contract signatures checking (#478)
  extrinsic-pool: use retain() (#613)
  rename Polkadot to Substrate in the license header via following four commands (#614)
  typo fixes (#608)
  RPC: Block number to block hash (#584)
  Minor fixes for nightly 2018-08-18 (#600)
  Time-based transaction banning (#594) (#602)
  cargo --force to allow CI to build. (#599)
  Fix logging (#587)
  Fix runtime version cache (#586)