Telnet poller hungs in the situation that file descripter is not ready forever.

Zabbix server uses the SIGARLM with alarm() for timeout by throwing the signal to itself. But Telnet poller uses select() in addition. select() does not warrant with signals.
In the situation, Telnet poller wait for file descripter become ready. But in the heavy load and etc. it does not become ready. So, Telnet poller receives SIGARLM. But if it calls select() then, it hungs!

I attached the patches for 2.0.7 and 1.8.17.