[Nut-upsuser] manual transfer switch to make UPS testing easier

[Ken Olum]

In case this is helpful to anyone, here's what I did to make it easier
to test NUT and my UPS.  My problem is that for testing I don't want my
system plugged into my UPS, so I can test UPS operations without
shutting down my system.  But the rest of the time, I want to be
protected against power problems.  My solution was to build a transfer
switch (just a DPDT switch in a box) that enables me to switch my system
between wall power and UPS power.  Thus I can connect the system to the
wall, shut down the UPS for testing, and connect my system back to the
UPS when I'm done, all without any system shutdowns.

                                        Ken