You had a 50/50 chance of getting it right. It sounds like things were done right based on your test. I'd always take the precaution of shutting off the power to the fixture prior to changing bulbs, etc... anyway.

I'm not sure about the WWII copper shortage. That's just the "story" I heard. Doesn't change the safety issue. Here's an excerpt from a website that attributes the 3 wire "legalization" to the post war housing boom. A little dubious because 1947 seems to fast after WWII for a housing boom. http://www.dli.mn.gov/ccld/PDF/eli_GFCI_history.pdf Circuit grounding was one of the more hotly contested topics in the early history of electrification. In the early 1890Âs, the New York Board of Fire Underwriters had condemned the practice of grounding the neutral as a dangerous practice, especially in a 3-wire Edison (120/240 Volt) system. The Edison utility companies, on the other hand, found just cause to ground their supply systems, even as others thought the utilities were doing this to just save copper and money at the cost of an increased fire risk. The great debate continued for over a decade, but in 1903 the Code was revised to recommend that these circuits be grounded, and finally in the 1913 Code a mandatory circuit grounding requirement was included for circuits like the popular residential Edison 3-wire system. The permission for neutral grounding, the practice of using the neutral conductor as an equipment grounding conductor, was first permitted in the 1947 Code for electric ranges. At around that time many electric utilities were promoting the use of residential 240 V cooking for the post WWII housing boom, and many were even offering to install an upgraded service to older homes at no charge. However, there were no NM cables available at the time with conductors of sufficient ampacity to handle these higher amperage branch circuits. There were, though, service entrance cables of sufficient size, but they had a bare neutral conductor. This special Code permission allowed the frames of these large appliances to be grounded through the uninsulated grounded neutral conductor of the Type SE service entrance cable used to supply the branch circuit. The use of neutral grounding was also extended to electric clothes dryers in 1953. However, almost 50 years later, this special permission for neutral grounding was taken away in the 1996 Code for all but existing branch circuit installations.

You can use anon-contact voltage tester for this. With the wires separated and not touching anything, turn the power on. Be VERY careful, and have someone else standing by to turn off the power and help you in case of an accident. Hold the tester's tip near each wire. The one that makes it buzz when it's further away is the hot wire. A more reliable method, in my experience, is to use a 2-wire neon tester, which is cheaper, but for some reason harder to find these days. With the light in the room somewhat subdued, touch one probe of the tester to the metal junction box, or pretty much anything metal nearby, and touch the other probe to each wire from the box in turn. The one that makes a faint glow in the tester is the hot wire.

Alternatively, there was no neutral to the outlet and some idiot decided to use the ground instead. As pointed out that high-impedence meters (which most are, what you want in most cases) will register induced voltages on long pieces of unterminated wire. You are right to be concerned, it is NEVER EVER proper to connect the neutral and ground together in an electrical box or on a receptacle. The test is simple here: Put the blacks on the brass screw, the whites on the silver screw, the ground on the green screw. If the outlet doesn't work properly, something is amiss ahead of this. You then have to go back to other places there may be junctions that have opened up or other damage. Chances are, unless you've got some experience with this, an electrician is the best answer.