Pass collations to functions in FunctionCallInfoData, not FmgrInfo.

Since collation is effectively an argument, not a property of the function,
FmgrInfo is really the wrong place for it; and this becomes critical in
cases where a cached FmgrInfo is used for varying purposes that might need
different collation settings.  Fix by passing it in FunctionCallInfoData
instead.  In particular this allows a clean fix for bug #5970 (record_cmp
not working).  This requires touching a bit more code than the original
method, but nobody ever thought that collations would not be an invasive
patch...

src/backend/utils/adt/ri_triggers.c

@@ -3963,7 +3963,10 @@ ri_AttributesEqual(Oid eq_opr, Oid typeid,
 								 BoolGetDatum(false));	/* implicit coercion */
 	}
 
-	/* Apply the comparison operator */
+	/*
+	 * Apply the comparison operator.  We assume it doesn't
+	 * care about collations.
+	 */
 	return DatumGetBool(FunctionCall2(&entry->eq_opr_finfo,
 									  oldvalue, newvalue));
 }