Update solution and C++ projects for VS 2013.
Fix bug with unlock scenario.
 - Fixes #227
New plugin: DriveMapper
  - Notification-based plugin
  - Should be a good companion to the SingleUser plugin.
  - Allows mapping of multiple drives at logon.
  - Uses user impersonation by pInvoking ImpersonateLoggedOnUser
  - Does impersonation in a separate thread for safety.