Domain should be always specified for transf. vector
Fix for non-saved domain for prediction vector.

The Model#scoreImpl method created a zero vector which included
DKV#put call, BUT then the domain was set up BUT the vector
was not put into DKV again.
Strategies for handlng missing cols in subframe call.

The method Frame#subframe can now throw IllegalArgumentException
if there is a missing column or replace missing column by a constant
column.