Merge branch 'tc/clone-single-revision'

Merge branch 'tc/clone-single-revision'

"git clone" learned to make a shallow clone for a single commit
that is not necessarily be at the tip of any branch.

* tc/clone-single-revision:
  builtin/clone: teach git-clone(1) the --revision= option
  parse-options: introduce die_for_incompatible_opt2()
  clone: introduce struct clone_opts in builtin/clone.c
  clone: add tags refspec earlier to fetch refspec
  clone: refactor wanted_peer_refs()
  clone: make it possible to specify --tags
  clone: cut down on global variables in clone.c