Merge branch 'rs/name-rev-memsave'

Memory footprint and performance of "git name-rev" has been
improved.

* rs/name-rev-memsave:
  name-rev: sort tip names before applying
  name-rev: release unused name strings
  name-rev: generate name strings only if they are better
  name-rev: pre-size buffer in get_parent_name()
  name-rev: factor out get_parent_name()
  name-rev: put struct rev_name into commit slab
  name-rev: don't _peek() in create_or_update_name()
  name-rev: don't leak path copy in name_ref()
  name-rev: respect const qualifier
  name-rev: remove unused typedef
  name-rev: rewrite create_or_update_name()