Merge branch 'jc/merge' into next

Merge branch 'jc/merge' into next

* jc/merge:
  git-merge knows some strategies want to skip trivial merges
  generate-cmdlist: style cleanups.
  Add missing semicolon to sed command.
  unpack_delta_entry(): reduce memory footprint.
  git.el: Added a function to diff against the other heads in a merge.
  git.el: Get the default user name and email from the repository config.
  git.el: More robust handling of subprocess errors when returning strings.