SSH2: Defer to default socket timeout in absence of more specific value

[rposky]

Attempting to address #2020, this issue formalizes the implied behavior prior to #1999 regarding PHP stream timeouts, by defaulting to PHP's default_socket_timeout for stream read functions when the user has not requested a timeout or keep-alive interval. This change mirrors the default timeout behavior of PHP socket streams, as evidenced here, and thus the behavior prior to #1999 changes, when stream_set_timeout was conditionally invoked. It is noteworthy that the prior implementation would not permit an update to remove a timeout via SSH2:setTimeout, given the conditional invocation of stream_set_timeout, now supported.

The following simple test confirms the underlying use of the default socket timeout when stream_set_timeout is never invoked, as execution terminates after 10 seconds, as defined.

<?php
$start = time();
ini_set('default_socket_timeout', 10);
$fsock = fsockopen('127.0.0.1', 22);
stream_get_contents($fsock);
printf("Time: %d", (time() - $start));

[terrafrost]

Looks good!

Also, apologies for the delay - I'm once again on vacation lol. I'm doing Black Hat USA in Vegas this week but left a few days early to do sight seeing.