Remove some innocent warnings

Remove the following warnings. They pop out when building with gcc 4.6.3 in x64, but don't cause any real problem.

    ntb-daemon.c: In function ‘daemonize’:
    ntb-daemon.c:288:16: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result]
    ntb-daemon.c:289:16: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result]
    ntb-daemon.c:290:16: warning: ignoring return value of ‘freopen’, declared with attribute warn_unused_result [-Wunused-result]

    ntb-mail-parser.c: In function ‘ntb_mail_parser_parse’:
    ntb-mail-parser.c:782:17: warning: ‘processed’ may be used uninitialized in this function [-Wuninitialized]

    ntb-quoted-printable.c: In function ‘ntb_quoted_printable_decode’:
    ntb-quoted-printable.c:212:17: warning: ‘processed’ may be used uninitialized in this function [-Wuninitialized]