Silence "may write a terminating nul past the end of the destination" warnings.
* gettext-tools/src/write-po.c (message_print_comment_filepos): Increase size of
buffer by 1.
* gettext-tools/src/xg-encoding.c (non_ascii_error_message,
non_utf8_error_message): Likewise.
* gettext-tools/src/xg-message.c (set_format_flags_from_context,
warn_format_string, remember_a_message): Likewise.
