security fixes:
    privilege escalation via mountpoint race conditions (CVE-2011-1831, CVE-2011-1832)
    race condition when checking source during mount (CVE-2011-1833)
    mtab corruption via improper handling (CVE-2011-1834)
    key poisoning via insecure temp directory handling (CVE-2011-1835)
    information disclosure via recovery mount in /tmp (CVE-2011-1836)
    arbitrary file overwrite via lock counter race (CVE-2011-1837)