Part of MAHOUT-1202.

Makes DoubleFunction and DoubleDoubleFunction abstract
classes and adds method for a function class that can speedup vector operations
that check if a function has certain properties (is associative/commutative
etc.)



git-svn-id: https://svn.apache.org/repos/asf/mahout/trunk@1478853 13f79535-47bb-0310-9956-ffa450edef68