Decouple CChain from mapBlockIndex
Move CBlockIndex, CChain and related code out of main
doc: Update SHA256SUMS.asc step in release-process.md

- The Hash: header is prepended by gpg, and states the hashing used by
  gpg, not what is used to hash the files

- Add more detailed steps
Merge pull request #4796

e8b5f0d Move CBlockIndex, CChain and related code out of main (jtimon)
6db83db Decouple CChain from mapBlockIndex (jtimon)
Merge remote-tracking branch 'bitcoin/master'