A few changes

- updated to NNLO ttbar x-section (245.8pb)
- trying to fix the JER issue: the data jets were smeared to 0, which shouldn't happen. also, if no generated jet was found, the jets were smeared to 0 in MC events as well. A little dirty fix should take care of this, but need to understand and correct it properly. See issue #61.
- added the JER systematic in start_2012_analysis.sh script
- added a suffix for output files with JER systematic applied
- some formatting changes