Sometimes to pass a variable number of argument we allocate an array, store
the arguments in that array, and then pass the array as the single C-level
arg.  This caused ref issues where the refcounter thought that the variables
were dead after the store -- ie before the function call -- and it would
decref them right then.  This commit adds a "refUsed" hook that allows us
to specify these sorts of "non-IR-based" uses.

Another option would have been to make the arrays fully refcounted (ie the
array itself is treated as owning references to its contents), but in this
case I think that's overkill since it's really just an ABI issue that the
refcounter didn't understand.