The TinyLFU test was failing for changes unrelated to anything in the tinyufo
crate. This changes the test to stop that! What was occurring was expected
behavior, so the test is what's changing instead of any internal logic.
What was happening were hash collisions in the bloom filter used by the
estimator. Instead of asserting that we'd always start counting from 0, we now
allow for this in the test by `get()`ing first, then comparing relative
values. For the final comparisons, we check that values are greater-than or
equal-to their lower bound as determined by the number of `incr()`s we called on
their keys.
