| I hate when a simple job turns into a nightmare. The confusing part is that you did exactly what should be done, turn off and on each circuit breaker. The possibilities are endless as to the problem. I need to ask you to turn off each breaker again, insuring that you firmly turn each off, and then back on, noting that one may trip in your hand.
Are the breakers labeled as to the circuit or area it covers? This would narrow down all the breakers to the one for this lighting circuit. If not, when you get this problem repaired, I recommend that this be your next project, as now you can see the benefit of having the breakers labeled properly.
There is a slim chance the main breaker is the culprit, unlikly, but will not hurt to turn this one off and on.
Where did you hear the pop come from? I suspect the wires inside the fixture is where the short is. Also, just occured to me, make sure all lighting switches are in the off position to help narrow down the short, before resetting the breakers.
I think the short still exists in the fixture and the switch for the light is on, and when you reset the breakers, one still detects the short and is tripping as you reset them and you may not be noticing.
Another thing you can do is to disconnect the fixture wires from the outlet box, to be sure if the short is in the fixture you have cleared the fixture from the circuit wiring.
Without tearing into the panel, this is about the best you can do for now. Opeing the panel to check the output of each breaker, hoping to find the one that is affecting the circuit is a risky chore, and you will need to have the skill to open and check inside.
Do the troubleshooting steps I have outlined so far, lets see if this can be solved before getting into the panel | 
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