(PUP-2881) Taskscheduler HRESULTs as 2s complement

 - When an HRESULT is returned from an FFI call to a COM method, the
   value is returned as an unsigned 32-bit integer.  It is a 2s
   complement style number that is typically -2XXXXXXXXX.  However, our
   HRESULT constants are defined in a way that doesn't ultimately
   represent them as 2s complement, which yields failures when giving
   them special treatment during error handling.  In other words, the
   errors we think we're ignoring are not actually being ignored,
   resulting in acceptance test failures.