Cmssw gitignore

Ignore everything in `CMSSW_5_3_11` except the following directories:
* `CMSSW_5_3_11/src/SingleTopPolarization`
* `CMSSW_5_3_11/src/data`
* `CMSSW_5_3_11/src/PhysicsTools`

Also ignore the `PatAlgos` and `PatUtils` packages in `PhysicsTools`, since they seem to be automatically downloaded.

It is interesting that the `CMSSW_5_3_11/config` is completely ignored, although it has files that are in the repo. However since it was explicitly ignored before, I did not change that behavior.

Finally, ignore the `exempi-2.2.1` directory and tar as well.