Log Message:
Update ptexenc to 1.3.1.

Changes:
    - ptexenc.c: Use kpse_readable_file() with non-const arg.
    - ptexenc/ptexenc.h: Correct set_enc_string() return type.
    - ptexenc.c (input_line2): Handle input files with Dos/Windows
      (CRLF) line endings.
    - Various sjisterminal related changes.
    - unicode-jp.c: Update variation[] table.