New test case "fotest" for fail-over of CBS to Freelist in MVFF. (Plus stub for MVT.) Need some testing hooks in MVFF and MVT for getting the CBS.
This reveals a couple of bugs in MVFF: (i) if CBSDelete fails, this might be because the block is actually on the Freelist instead; (ii) we can't SegFree before calling FreelistDelete because the Freelist needs access to the memory in order to read its pointers.