Fix issue where Analyze produces noise estimate that's too low.
Fix issue where Analyze produces noise estimate that's too low.

See https://github.com/BitFunnel/BitFunnel/issues/347 for more discusison.  Note
that this code needs a cleanup commit before getting commited to trunk.

danluu/BitFunnel,BitFunnel/BitFunnel,danluu/BitFunnel,danluu/BitFunnel,danluu/BitFunnel,BitFunnel/BitFunnel,BitFunnel/BitFunnel,BitFunnel/BitFunnel,danluu/BitFunnel,BitFunnel/BitFunnel,danluu/BitFunnel,BitFunnel/BitFunnel