Conversion from unsigned char sha1[20] to struct object_id
continues.

* bc/cocci:
  diff: convert prep_temp_blob() to struct object_id
  merge-recursive: convert merge_recursive_generic() to object_id
  merge-recursive: convert leaf functions to use struct object_id
  merge-recursive: convert struct merge_file_info to object_id
  merge-recursive: convert struct stage_data to use object_id
  diff: rename struct diff_filespec's sha1_valid member
  diff: convert struct diff_filespec to struct object_id
  coccinelle: apply object_id Coccinelle transformations
  coccinelle: convert hashcpy() with null_sha1 to hashclr()
  contrib/coccinelle: add basic Coccinelle transforms
  hex: add oid_to_hex_r()