od: zero-fill input to required byte length

[mknos]

• I noticed that when the number of input bytes is odd, the output of od -x is incorrect
• This was because unpack('S', $data) returns nothing if $data is 1 byte
• Standard od zero-fills the 16 bit number
• The do-remainder-bytes logic is incorrect (tangled web of pack, unpack and substr)
• float() and long() require input to be zero-filled 32-bits
• udecimal(), decimal(), octal2() and hex() require input to be zero-filled 16-bits
• Patch tested on amd64 against GNU od

Original output which uncovered this:
$ perl hexdump test
00000000 c6 f3 |..|
$ od -j 1 -x test # gnu od
0000001 00f3
0000002
$ perl od -j 1 -x test
00000001 0001
00000002

Also without -j:
$ xxd in2
00000000: d8ab 7a ..z
$ perl od -x in2
00000000 abd8 0000
00000003

[briandfoy]

I see this, but I'm about to leave for a couple weeks so I'll deal with it when I get back.