NMS-4763 Win2008R2 WMI TS stats fix and NMS-6822 add WMI disk/memory data collection

This pull request addresses the following two JIRA tickets:

1. A fix for a tracking Terminal Server sessions in Windows Serer 2008 and later; the upstream code only handles the Windows 2003 case:
"NMS-4763: Datacollection for Terminal Services on W2K8+", http://issues.opennms.org/browse/NMS-4763

2. The addition of additional WMI-based performance statistics for Windows:
"NMS-6822: Add WMI data collection and graphs for paging, disk I/O, and total memory", http://issues.opennms.org/browse/NMS-6822