Cve 2014-4113 x64 Support For Windows 6.1

This PR adds 64-bit support for the CVE-2014-4113 exploit for Windows 6.1 (Windows 7 SP1 & Windows 2008 R2 SP1). This also takes a first crack at adding a more robust check routine.

The x86 and x64 targets are broken out separately, this was so the module would use a compatible payload. It appears as though even when the target is set to Windows x64 a 32-bit payload can still be selected which causes notepad to crash and the exploit to fail. I'm hoping someone will have an idea on how to ensure that the payload is of a compatible arch.

Thanks @jvazquez-r7!
I know it is a pain to write a check having into account every patched system! I think something like:

```
    # Neither target supports Windows 8 or 8.1
    return Exploit::CheckCode::Safe if build == 9200
    return Exploit::CheckCode::Safe if build == 9600

    if arch == ARCH_X86
      return Exploit::CheckCode::Detected if [2600, 3790, 7600].include?(build)
    else
      return Exploit::CheckCode::Detected if build == 7601
    end

    return Exploit::CheckCode::Unknown
```

Could be good enough atm :)