Merge branch 'jc/mailinfo' into next

Merge branch 'jc/mailinfo' into next

* jc/mailinfo:
  mailinfo: skip bogus UNIX From line inside body
  tutorial-2: typofix in examples.
  tutorial: add discussion of index file, object database
  tutorial: expanded discussion of commit history
  tutorial: replace "whatchanged" by "log"
  NO_INET_NTOP and compat/inet_ntop.c for some systems (e.g. old Cygwin).
  remove superflous "const"
  checkdiff_consume: strtol parameter fix.
  Elaborate on why ':' is a bad idea in a ref name.
  Reference git-check-ref-format in git-branch.