Support TCP_NODELAY for stream-based connections on PHP >= 5.4.0.

This cannot be implemented for previous versions of PHP because we
need socket_import_stream() to extract the underlying socket resource
from the stream in order to be able to set the TCP_NODELAY flag.
Fix unserialization of Predis/Connection/PhpiredisStreamConnection.
No need for strict comparison here.

Should be also slightly faster (at least on a micro-optimization scale).