In _git-show, remove calls to __git_commits and __git_tags.
  Rationale: 'commits' and 'tags' are already added by __git_trees.
  Adding them twice makes `zstyle ... tag-order` give unexpected
  results.

In __git_recent_commits, remove the line that adds 'heads'.
  Rationale: The completion for most subcommands already adds
  'heads-local' and 'heads-remote'. Adding an additional 'heads' inside
  __git_recent_commits results in heads being listed twice in two
  separate groups.


By the way: Why is there a `(( $+functions[_git-XXX] )) ||` statement
in front of each function inside Completion/Unix/Command/_git ? Can
those be removed?


Patch attached, below.