Merge branch 'maint'

* maint:
  Have sample update hook not refuse deleting a branch through push.
  variable $projectdesc needs to be set before checking against unchanged default.
  Update git-annotate/git-blame documentation
  Update git-apply documentation
  Update git-applymbox documentation
  Update git-am documentation
  user-manual: use detached head when rewriting history
  user-manual: start revising "internals" chapter
  user-manual: detached HEAD
  user-manual: fix discussion of default clone
  Documentation: clarify track/no-track option.
  Documentation: clarify git-checkout -f, minor editing
  Documentation: minor edits of git-lost-found manpage