This commit introduces a new option, app:capture, which can be set to
either DXGI or NvFBC to force the host application to use that backend.
This is very useful for testing DXGI on Quadro cards, which would default
to running with NvFBC.
This will allow us to add an option to disable the screensaver on the client
when an application in the guest requests it. This behaviour may be useful
when the guest is doing media playback.
This makes it a compile-time error to call a function that semantically
takes no parameters with a nonzero number of arguments.
Previously, such code would still compile, but risk blowing up the stack
if a compiler chose to use something other than caller-cleanup calling
conventions.
