...to only work with LONG values, as it is only used to compare enumerator
values.  (But keep its general defensive-programming air that's so prevalent
across the idlc code base; not sure whether it could rightfully be tightened, or
whether this might be needed in parser's error recovery.)

Change-Id: I15f1700834f9397f3c2e0ffdb00e2abeecb734f9