add aggregation functions including corr, covar,regr-slope, regr-interce...

add aggregation functions including corr, covar,regr-slope, regr-intercept and unit tests.

I only leave the Double and Double version and most unit tests failed. 
and then I comment out the Long input function in VarianceAggregation and then run TestLongVarianceAggregation, and most unit tests failed. 
![screenshot 2014-12-03 14 38 13](https://cloud.githubusercontent.com/assets/9942972/5290248/0cb8e054-7afa-11e4-9cce-197594602b34.png)