Sorting.indexSort overload for the Float array

It was missing orginally
Merge pull request #322 from eiennohito/patch-1

Sorting.indexSort overload for the Float array
cdfs and inverse cdfs for the easy tests
tests for HasCdf
an actual cdf function!
Merge remote-tracking branch 'scalanlp/master'
actually use the implicit random number generator. closes #319
added a “mapActive” method to zipMapKeyValues, should be faster for OWLQN (#326).

Also optimized zipMap for SparseVector when f(0, 0) == 0.
missed an exp in NegativeBinomial
use gallop search instead of binarySearch for dot products. much faster in nearly all cases
benchmarks for SparseVector#dot
so linear search for small arrays doesn’t seem to help
switch between “smart” loop for big sparse vectors, and simple loop for small ones
Merge branch 'master' of https://github.com/scalanlp/breeze into signal