TupleBatch: add constructor that gets num_tuples from the columns
TupleBatch: add constructor that gets num_tuples from the columns

The sanity checking happens in the other constructor anyway.

Signed-off-by: Daniel Halperin <1a02732a15f637c31107256cbee5819e36aa7c67@cs.washington.edu>

bsalimi/myria,bsalimi/myria,uwescience/myria,uwescience/myria,uwescience/myria,jamesmarva/myria,jamesmarva/myria,jamesmarva/myria,bsalimi/myria