Introducing a new union member in Tcl_Obj is not a good idea in a patch release, especially using "long". 
Better allow iterNum and iterMax to grow to ssize_t (or size_t) in Tcl 9 (or 8.x, why not?). 
Usage of "long" in public API causes interoperability problems between Cygwin64 and Win64 (probably no-one cares except me).
Oops, wrong macro.