tests/fs.ml: create a file with 2 blocks (exposing a bug in the process)
tests/fs.ml: create a file with 2 blocks (exposing a bug in the process)

somehow, when we truncate a file to be 2 blocks long, both of the blocks
in that inode end up pointing to the same physical block on disk!  probably
the allocator is broken and returns the same block repeatedly..

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