Increase default allowed memory usage for better compression.
Increase default allowed memory usage for better compression.

The reality is that the memory usage doesn't ever hit the max due to
failures in the hashing approach; however, these changes *do* ensure
there is a better utilization of the hash w/out impacting memory
utilization for the most part.

Effectively, for 2 100MB files, we utilize a <300MB of ram at max,
but get a 1.5% improvement- both uncompressed and compressed- due to
the increased matching.

It's a workaround for flaws in the rh bucket implementation, but it's
usable and worth the addition (especially since hash size is configurable
via commandline).

ferringb/diffball,ferringb/diffball