Properly handle auto-enum conversion

Can now set toEnum=true, and the response will be treated as a
categorical (and the model-build will do classification), and any temp
enum column will get cleaned up when an enclosing Scope.exit() happens.
init(expensive): only do expensive checks if true (means: trainModel()
was called and the user expects things will be slow) vs false (means:
called on a GUI click; fast checks only; GUI is waitnig for a quick
response)
Turn on some basic GBM tests.
GBM reports R^2 value during scoring, instead of MSE.
GBM builds ConfusionMatrix and AUC if appropriate.
Merge branch 'master' of github.com:0xdata/h2o-dev

Conflicts:
	h2o-algos/src/main/java/hex/deeplearning/DeepLearning.java
Merge branch 'master' of github.com:0xdata/h2o-dev
default init flag
Merge branch 'master' of github.com:0xdata/h2o-dev
Merge branch 'master' of github.com:0xdata/h2o-dev
Merge branch 'master' of github.com:0xdata/h2o-dev
Merge branch 'master' of github.com:0xdata/h2o-dev
Merge branch 'master' of github.com:0xdata/h2o-dev
Merge branch 'master' of github.com:0xdata/h2o-dev