Merge branch 'jc/cat-file-batch-commands'

"git cat-file" learns "--batch-command" mode, which is a more flexible interface than the existing "--batch" or "--batch-check" modes, to allow different kinds of inquiries made. * jc/cat-file-batch-commands: cat-file: add --batch-command mode cat-file: add remove_timestamp helper cat-file: introduce batch_mode enum to replace print_contents cat-file: rename cmdmode to transform_mode