TestCommitLog segment size dtests fail on trunk

The test for the commit log segment size when the specified size is 32MB. It fails for me locally and on on cassci. (cassci link)

The command to run the test by itself is CASSANDRA_VERSION=git:trunk nosetests commitlog_test.py:TestCommitLog.default_segment_size_test.

EDIT: a similar test, commitlog_test.py:TestCommitLog.small_segment_size_test, also fails with a similar error.

The solution here may just be to change the expected size or the acceptable error – the result isn't far off. I'm happy to make the dtest change if that's the solution.