Rewrite of EtaCorrection method, and improved resolution for s2x2y2 clusters. 

See commit comments. Plots here show the EtaCorrection and maxTOT reslutions for s2x2y2 clusters. 

![resx_s2x2y2_etac](https://cloud.githubusercontent.com/assets/8256377/4152703/4619bf66-3451-11e4-8a66-c1685f6927e6.png)
![resx_s2x2y2_maxtot](https://cloud.githubusercontent.com/assets/8256377/4152705/4a01184a-3451-11e4-8fa7-983d5fd2b9d8.png)