Updated handling of appendables in MRTask2. Appendable Vecs are kept separate from normal Vecs so they can be passed directly instead of via K/V stored and roolups can be computed in standard M/R way.

Vector separation is kept also in map calls, which now have inputs (Chunks) and outputs(NewChunks) separated.
Also, users do not directly create Appendable Vecs, they simply tell MRTask how many output vectros they want to create.
Merge branch 'master' of github.com:0xdata/h2o
Updated GLM2 to work with updated MRTask (no overriding of the dfork!)
Merge branch 'master' of github.com:0xdata/h2o