Updating btag weights in unfolding workflows in line with changes in BAT.

Changes have been tested, btagweight plots from the output files from running unfoldingBLT_cfg.py on TTJets datasets are below:
Previous method, 7TeV:
![original_7tev_screen shot 2014-10-02 at 09 59 50](https://cloud.githubusercontent.com/assets/2691839/4489754/4ae517c2-4a20-11e4-80be-117f205923cc.png)
New method, 7TeV:
![new_7tev_screen shot 2014-10-02 at 10 01 46](https://cloud.githubusercontent.com/assets/2691839/4489756/4f07e03c-4a20-11e4-90bd-ee0617b341fc.png)
Previous method, 8TeV:
![original_8tev_screen shot 2014-10-02 at 10 00 48](https://cloud.githubusercontent.com/assets/2691839/4489759/52780b70-4a20-11e4-85e5-b274e7d90f36.png)
New method, 8TeV:
![new_8tev_screen shot 2014-10-02 at 10 01 20](https://cloud.githubusercontent.com/assets/2691839/4489760/54060104-4a20-11e4-9e82-bf5b1054c2fe.png)

I think these follow the trends we are expecting.