inconsistency with --abbrev=0

[Markus Heidelberg <markus.heidelberg@web.de>]

The minimum (>=4) number of chars is shown by

  git log|show|whatchanged --abbrev-commit --raw --abbrev=0
  git rev-list --abbrev-commit --abbrev=0 HEAD
  git show-ref --abbrev=0
  and the various diff commands

All 40 are shown by

  git branch -v --abbrev=0
  git ls-files --stage --abbrev=0
  git ls-tree --abbrev=0 HEAD

The latter group uses parse-options and doesn't set abbrev to 4 in this
case. This is needed for git-describe to omit the output of the commit.

What should --abbrev=0 behave like?

Markus