Implement multiple row lookup by default

Performing multiple sequential row lookups can be inefficient,
so try to simplify the implementation of batching here by pushing
it down into the GenericSchema.

Change-Id: I770e8690d48ea1c22cb55f96dd636498b5a938bc
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed