Implemented simple cache for Nxlog(N) calculations when N is an integer in ContingencyTables. This seems give some nice speed-ups for REPTree and other classes that use the entropy calculations from ContingencyTables.

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka/trunk@10042 e0a1b77d-ad91-4216-81b1-defd5f83fa92
Some small changes to AbstractInstance and RandomTree to (hopefully) make things run just a tiny bit faster.

git-svn-id: https://svn.cms.waikato.ac.nz/svn/weka/trunk@10044 e0a1b77d-ad91-4216-81b1-defd5f83fa92
Merge remote-tracking branch 'upstream'