re-adding tutorial
Comment out stuff that is breaking the compile.
Fix a non-obvious javac bug.

javac 1.6. wrongly recognizes the context of this pointer in a
constructor of class. javac 1.7/eclipse javac were ok.
change some names to show it's doing exec conversions
Use the username for tunneling instructions in case -name was used.
Extend NN Iris test to include holdout_ratio, and pass the RNG to the reference
implementation.  Also check for relative errors.
Remove unnecessary initial randomization of output layer. Also use an atomic
RNG seed.
Enable warmup samples input, use 1000 per default.  Disabled for MapReduce mode
on > 1 nodes.
Speedup NN by improving detection and reporting of numerical instabilities
without overhead in the Layer code.
Add link "Predict!" to NN model page.
Add general class for D3 visualization of 2D scatter plots, taken from PCA, and
use it for NN's classification errors.
TODO: PCA and GBM could use this new class instead of their inline code.