Merge branch 'jc/name-rev-exact-ref'

Corrects the longstanding sloppiness in the implementation of
name-rev that conflated "we take commit-ish" and "differences
between tags and commits do not matter".

* jc/name-rev-exact-ref:
  describe: fix --contains when a tag is given as input
  name-rev: differentiate between tags and commits they point at
  describe: use argv-array
  name-rev: allow converting the exact object name at the tip of a ref
  name-ref: factor out name shortening logic from name_ref()