Create binary Spark distribution

This creates a new packaging target, a binary Spark distribution.  The existing scripts should continue to work with existing packaging (ie sbt package; run.....)

1) A new script, `make-distribution.sh`, creates a binary distro in dist/
2) The dist/ folder contains no sources, just a single assembly jar (for now), along with bin/ and conf/, and the run and spark-shell scripts.
3) The run script has been modified to support both the existing distro and the new binary distro.  The existing classpath logic has been split out to a new file, and the run script size has been cut by half.

The binary-only distribution makes deploys much easier, as it already contains Scala and all other dependencies packaged together.   Once you create the distribution, one could simply rsync the distro folder to the cluster, configure spark, and run the start scripts.
- spark-shell runs on the cluster without Scala installed (and restores echo properly)
- the "ps" output is much cleaner since the classpath will be much shorter

I also sneaked in a small addition to spark-shell to add convenient flags.

Caveats:
 - docs have not been updated yet
 - currently bagel, streaming, and the examples are excluded from the distro.