cups-driverd did not use the LanguageEncoding attribute in PPD

cups-driverd did not use the LanguageEncoding attribute in PPD
files to convert the NickName to UTF-8 (STR #1503)

cups/libcups_s.exp:
    - Add _ppdGetEncoding.

cups/ppd.c:
    - Change static ppd_get_encoding to private _ppdGetEncoding
      function.

scheduler/cups-driverd.c:
    - load_ppds(): Load LanguageEncoding and convert NickName to
      UTF-8.

git-svn-id: svn+ssh://src.apple.com/svn/cups/cups.org/trunk@5333 7a7537e8-13f0-0310-91df-b6672ffda945