Add bloom filter

Very basic, but seems to do the job.

Signed-off-by: Jens Axboe <axboe@fb.com>
dedupe: default to using a bloom filter to save memory

With the bloom filter, we can comfortably check devices up to
the petabyte range, which isn't feasible if we track each
extent.

Signed-off-by: Jens Axboe <axboe@fb.com>
Add debug helper stub for t/ programs

Signed-off-by: Jens Axboe <axboe@fb.com>
t/lfsr-test: fixup time

Signed-off-by: Jens Axboe <axboe@fb.com>
dedupe: fix warning and segfault on -B0

Signed-off-by: Jens Axboe <axboe@fb.com>