Deprecated the emulation of '__le' using '__lt'

As hinted in the manual for Lua 5.3, the emulation of the metamethod
for '__le' using '__le' has been deprecated. It is slow, complicates
the logic, and it is easy to avoid this emulation by defining a proper
'__le' function.

Moreover, often this emulation was used wrongly, with a programmer
assuming that an order is total when it is not (e.g., NaN in
floating-point numbers).

lvm.c

@@ -754,10 +754,12 @@ void luaV_finishOp (lua_State *L) {
     case OP_EQ: {  /* note that 'OP_EQI'/'OP_EQK' cannot yield */
       int res = !l_isfalse(s2v(L->top - 1));
       L->top--;
+#if defined(LUA_COMPAT_LT_LE)
       if (ci->callstatus & CIST_LEQ) {  /* "<=" using "<" instead? */
         ci->callstatus ^= CIST_LEQ;  /* clear mark */
         res = !res;  /* negate result */
       }
+#endif
       lua_assert(GET_OPCODE(*ci->u.l.savedpc) == OP_JMP);
       if (res != GETARG_k(inst))  /* condition failed? */
         ci->u.l.savedpc++;  /* skip jump instruction */