Make scaling out a feature for merge.py.

This is a simple implementation designed to work with our current
non-HOT approach. We need to adjust our templates a little to support
this - though future work could make that better, it's orthogonal to
this effort.

Change-Id: I555617e5f24a5882de915f057dc02e008c81e753
Merge "Make scaling out a feature for merge.py."