OK, I figured out how to do what I wanted. I am planning to connect a regulated power supply that provides ~3.3VDC. The main thing I had to figure out was how to configure the PCB when neither a battery booster nor a regulator are needed. I think either shorting the REG pin and shorting the regulator or shorting the BAT pin and shorting the battery booster would each achieve the desired result.
Best posts made by cmrockwell
RE: 💬 Easy/Newbie PCB for MySensors
RE: Which Arduino IDE version?
I am a relatively new user to MySensors, and I think a bug such as this needs to be described on the main page on how to build an Ethernet Gateway. This problem caused me a lot of frustation, and I don't know enough about how the hardware works to even realize that my gateway was being reset every 2 seconds. Anyone trying to build a W5100 ethernet gateway with a fresh Arduino install is going to experience this bug, and I think it will reflect poorly on the whole MySensors project if this bug is not highlighted on the build page.
The biggest benefit of the MySensors project is that getting up and running is relatively easy, but bugs such as this definitely make it harder.