sandbox.h

        when they're preempting another GPU job.
        The problem was as follows:
        - job A is chosen to preempt job B
        - we tell job B to quit, and initialize job A but don't start it;
            however, we set if scheduler state to SCHEDULED
            (rather than UNINITIALIZED)
        - job B exits, and we start job A.
            Since its state is not UNITIALIZED, we don't set up its slot dir.
        - job A runs in an empty slot dir, doesn't find its files, and bombs out.
    - client: add <slot_debug> option (prints messages about
        allocation of slots, creating/removing files in slot dirs).

svn path=/trunk/boinc/; revision=18217