Fix build on Windows 8 RTM
Fix build on Windows 8 RTM

Ref class destructors are now required to be virtual.

roryok/SQLite3-WinRT,roryok/SQLite3-WinRT,doo/SQLite3-WinRT,roryok/SQLite3-WinRT,doo/SQLite3-WinRT,roryok/SQLite3-WinRT,doo/SQLite3-WinRT