If you're absolutely sure that you smell coolant out of your exhaust pipe, then that means it's leaking into one or more combustion chambers, getting burned up and emitted out of the exhaust. The only two possible ways that antifreeze will make its way into those chambers on its own is a 'blown' head gasket or intake manifold gasket. All that means is that one of those gaskets are damaged or worn in a specific location. The symptoms can vary by the location of the gasket damage, as well as the severity of the damage. Sometimes, the damage is only between the coolant channel and combustion chamber. This means that coolant is leaking into the engine, but not into the oil. That means you won't find oil in water or water in oil. That sounds like what's going on here. It also sounds like the damage is small enough that the leak is slow, which could explain why you're not seeing a bunch of white smoke out of the exhaust; just smelling it. Paulster2 is correct here about the fact that it's just a matter of time before it gets worse, as well as testing for hydrocarbons in the coolant to confirm a gasket problem. You could do a pressure test, too, but the former will definitely be conclusive. Also, I agree that you should completely flush the mixture of standard and extended life coolant out of the system completely. I know it was probably an accident, but they're not meant to mix as they are chemically different, resulting in reactions that can be problematic, like the sludge Paulster2 mentioned. Anyway, to sum up, head gasket failure is more common but intake gasket failure is the only other way exhaust could smell like coolant, especially if oil and coolant aren't mixing. Good luck.
Edit: By 'on its own', I meant without mixing with oil in case there was any confusion. There's more ways for it to end up in combustion chambers in that case. Bad oil cooler + problem causing oil to burn in chambers, cracked head or engine block and possibly more. I suppose it's possible for a cracked head to be cracked in such a way that coolant is leaking into chambers but not oil but, in my experience, this is extremely rare.