More driver uninstallation concerns

[Troy Crosley <troycrosley@xxxxxxxxx>]

When the boot drivers (xenbus.sys, xenfilt.sys, xendisk.sys, xenvbd.sys) are uninstalled, they continue to be loaded at the next boot due to still having entries in HKLM\SYSTEM\CurrentControlSet\Services. However, Windows adds a "StartOverride" registry key for boot drivers that don't acquire any hardware to prevent them from being loaded during subsequent boots. This happens to all the drivers except xenfilt.sys, which continues to load during all subsequent boots after being uninstalled (and also seems to cause xen.sys to load as well).

xenfilt.sys will no longer load if it is removed from the registry as an upper filter for the HDC and System classes. I wasn't able to use the inf to modify those registry entries, so my solution was to use the coinstallers. I could submit a patch for these changes if they are desired.

Also, I noticed my previous patch for the coinstaller was accepted, but the other coinstallers ought to have the same fix applied--I could submit those patches as well.