od: align multiple -t specs

od: align multiple -t specs

* src/od.c (struct tspec): Add pad_width field, and adjust
print_function prototype.
(decode_one_format): Rewrite all fmt_string values to account for
pad width.
(FMT_BYTES_ALLOCATED): Adjust to new format style.
(main): Compute pad width per spec.
(write_block): Account for pad width.
(dump): Don't print padding-only fields.
(PRINT_TYPE, print_named_ascii, print_ascii): All print functions
adjusted to use variable pad width.
* tests/Makefile.am (TESTS): Add test.
* tests/misc/od-multiple-t: New file.
* THANKS: Update.
* NEWS: Mention the improvement.
Reported by Gary Johnson.