Merge branch 'jk/cat-file-batch-all'

"cat-file" learned "--batch-all-objects" option to enumerate all
available objects in the repository more quickly than "rev-list
--all --objects" (the output includes unreachable objects, though).

* jk/cat-file-batch-all:
  cat-file: sort and de-dup output of --batch-all-objects
  cat-file: add --batch-all-objects option
  cat-file: split batch_one_object into two stages
  cat-file: stop returning value from batch_one_object
  cat-file: add --buffer option
  cat-file: move batch_options definition to top of file
  cat-file: minor style fix in options list