'lua_State.nci' must be an integer

Lua can easily overflow an unsigned short counting nested calls.
(The limit to this value is the maximum stack size, LUAI_MAXSTACK,
which is currently 1e6.)

ltests.h

@@ -152,9 +152,12 @@ LUA_API void *debug_realloc (void *ud, void *block,
 */
 
 
-/* make stack-overflow tests run faster */
+/*
+** Reduce maximum stack size to make stack-overflow tests run faster.
+** (But value is still large enough to overflow smaller integers.)
+*/
 #undef LUAI_MAXSTACK
-#define LUAI_MAXSTACK   50000
+#define LUAI_MAXSTACK   68000
 
 
 /* test mode uses more stack space */