Dense/sparse sparse-chunk constructors

Move from a sparse NewChunk to a Sparse Chunk (either CX0Chunk or
CX2Chunk) without ever blowing out the size.
Add tests of the same.
Handle broken last line on a sparse column
some stuff for DRF2 testing.
increased compresssion for the gz testing (less 1s)
DRF model adaptation test.

The similar test as it is used for GBM but more finegrained.
Fix tests that peek into the guts of NewChunk

Fix sparse/dense bitvector path
Merge branch 'master' of github.com:0xdata/h2o
increase # of cols on tree stuff (2)
update
clean up Summary2 to have new Json schema; R wrappers updated, JUnit updated.
Merge branch 'master' into summary2