Merge branch 'jc/mktree'

Merge branch 'jc/mktree'

* jc/mktree:
  mktree: validate entry type in input
  mktree --batch: build more than one tree object
  mktree --missing: updated usage message and man page
  mktree --missing: allow missing objects
  t1010: add mktree test
  mktree: do not barf on a submodule commit
  builtin-mktree.c: use a helper function to handle one line of input
  mktree: use parse-options
  build-in git-mktree