Merge branch 'jc/hash-object'

"hash-object" learned a new "--literally" option to hash any random
garbage into a loose object, to allow us to create a test data for
mechanisms to catch corrupt objects.

* jc/hash-object:
  hash-object: add --literally option
  hash-object: pass 'write_object' as a flag
  hash-object: reduce file-scope statics