fix one bug in FS.v where we had confused the two allocators
fix one bug in FS.v where we had confused the two allocators

we were swapping the inode and block bitmap allocators in FS.create and FS.delete.
unfortunately the bug still persists!

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl