No more field 'lua_State.stacksize'

The stack size is derived from 'stack_last', when needed. Moreover,
the handling of stack sizes is more consistent, always excluding the
extra space except when allocating/deallocating the array.

lvm.c

@@ -1151,7 +1151,7 @@ void luaV_execute (lua_State *L, CallInfo *ci) {
     StkId ra;  /* instruction's A register */
     vmfetch();
     lua_assert(base == ci->func + 1);
-    lua_assert(base <= L->top && L->top < L->stack + L->stacksize);
+    lua_assert(base <= L->top && L->top < L->stack_last);
     /* invalidate top for instructions not expecting it */
     lua_assert(isIT(i) || (cast_void(L->top = base), 1));
     vmdispatch (GET_OPCODE(i)) {