Updated GLMVA to have more fine grained canceling during cholesky decomp. This is to make canceling work in cases with very large number of categoricals. Previously, GLM would only check for cancellation before and after cholesky is computed, but not during cholesky itself, which can take very long time and use all of the cpus.

Also added reporting of the size of the largest categorical at glm start.
Merge branch 'master' of github.com:0xdata/h2o