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 changed it to the logic you proposed in 830f631. You're correct though, it shouldn't have covered every build. The revision of 18577 should have just been for build 7601. I got the number 18577 as the last version of win32k.sys before the patch was installed.