- Use the Codec instead of Aliases in Python Standard Encodings

https://docs.python.org/2.7/library/codecs.html#standard-encodings
- Distinguish decoded data and data
- Make debug print conditionally
Ignore error in marshalled data if Perforce file type is utf16

Because the value of "Code" in marshalled data is often "error", which is
"CANNOT TRANSLATE" error message [1] with "p4 print",
if Perforce file type is utf16. But the missing data will be handled properly
in the streamOneP4File method with "p4 print -o".

  [1]
  Internationalization Notes for P4D, the Perforce Server and Perforce
  client applications
  http://www.perforce.com/perforce/doc.current/user/i18nnotes.txt