Add Unittests for new components

This adds some unit tests for the TBB based processing pipeline.

**Note:** this contains [Integrate the TBB based file processing into the Spooler](https://github.com/cvmfs/cvmfs/pull/220)
**Note:** this contains [New File Processing Pipeline based on TBB](https://github.com/cvmfs/cvmfs/pull/219)
**Note:** this contains [Add a Buffer template to util.h](https://github.com/cvmfs/cvmfs/pull/218)