Merge branch 'stable-2.10' into stable-2.11

* stable-2.10:
  Update 2.10.3 release notes
  Improve the version computation for the release notes
  Check reachability from R_HEADS/R_TAGS/REFS_CONFIG when creating branches
  Update 2.10.3 release notes
  Include submitter in ChangeMessage on submission
  Support hybrid OpenID and OAuth2 authentication
  Release notes for Gerrit 2.10.3

Change-Id: I03e0cbb444e9ae2090f510d6f4e49c6db5ece033