Merge pull request #15 from shivaram/v2

Add github.com to known_hosts
New images
Merge pull request #16 from shivaram/v2

Use a known github hostkey instead of keyscan
Update build process based on Spark changes
Merge pull request #20 from pwendell/build-changes

Update build process based on Spark changes
Adding 0.8.0 Spark version.
Merge pull request #21 from pwendell/v2

Adding 0.8.0 Spark version.
Adding 0.8.0 Shark (SNAPSHOT) version
Use 'return' instead of 'exit' in module init/setup scripts.

Previously, the exits were causing the top-level setup.sh
script to exit prematurely, which broke the --resume flag;
see SPARK-919.
Merge pull request #22 from JoshRosen/spark-919

Use 'return' instead of 'exit in init & setup scripts (SPARK-919)
Set SPARK_PUBLIC_DNS in spark-env.sh.

This addresses SPARK-833, an issue where Spark web UIs might
be bound to non-public addresses when running on EC2.  We solved
this problem for the Master and Worker UIs, but SPARK_PUBLIC_DNS
needs to be set in the driver's environment in order for the
application web UI to bind to the correct public address.

Some drivers, like programs run through `sbt run` or IPython
notebook, will need to `source spark-env.sh` or otherwise
copy its SPARK_PUBLIC_DNS setting.  This commit ensures that
SPARK_PUBLIC_DNS is set properly for programs run through
`pyspark` and the `run-example` scripts.
Merge pull request #23 from JoshRosen/spark-833

Set SPARK_PUBLIC_DNS in spark-env.sh (to address SPARK-833)
Adding Shark 0.7.1 version
Add RAM heuristics for larger heap sizes.

This patch leaves large amounts of free RAM for very large heaps.
This allows intermediate data to fit in buffer cache, even
for bigger shuffles.
Fix a bug in computing memory requirements