MAHOUT-77 speedups

[Grant Ingersoll]

I'm doing some more profiling and it seems like all over the place we  
are looping from i = 0; i < size() and calling getQuick.  This is  
then, for SparseVector, dominated by the find lookup, which is taking  
up a lot of time.

So, it's not that find() is slow, but the fact that we are needlessly  
calling getQuick() for loops.

Just an FYI as we go forward not to do that.

-Grant