Add CVE-2014-4971 BthPan local privilege escalation

Add CVE-2014-4971 BthPan local privilege escalation for Windows XP SP3.

This module incorporates the feedback we have gotten so far on pull request 3534 for a different module; if there is more, we will update this code accordingly as well.
I think that a more useful message than "Enjoy" would be good here, something inline with what the other local exploits do.