Merge branch 'vd/cat-file-objectmode-update'

"git cat-file --batch" learns to understand %(objectmode) atom to allow the caller to tell missing objects (due to repository corruption) and submodules (whose commit objects are OK to be missing) apart. * vd/cat-file-objectmode-update: cat-file.c: add batch handling for submodules cat-file: add %(objectmode) atom t1006: update 'run_tests' to test generic object specifiers