2 updates:
  1) updated MRTask2 not to close appendables automatically but upon user request (outputFrame() call) and requesting column names and DOMAINS to do that so that the vecs are stored with proper domains.

2) tiny update to slicing,  make slicing work just using arrays for indexes. Needs redo for big data.
Udpated fvec test to work with updates in MRTask2
Merge branch 'cliffc-eq2' of github.com:0xdata/h2o into cliffc-eq2