[AGENT++] Prevent inheriting file descriptor of the opened sockets to child processes

[Jochen Katz]

Hi,

> An application that uses SNMP++ can have problems when spawning new
> processes. The child process(es) inherit file descriptor of the
> currently running SNMP agent.
> 
> To fix this set *FD_CLOEXEC* flag while opening the sockets.

I have added a modified version of your patch (moved code to a function)
for the next release.

To answer your question in your other mail: You used the preferred way
to send patches.

Thanks and regards,
  Jochen