netlink: remote I/O

Proxy netlink packets through network using ZMQ. Use two connections:
 * PUSH/PULL — send requests to the server
 * PUB/SUB — receive netlink events

Also:
 * remove socket reference from marshal class
 * private attribute names
netlink: catch interrupts while getting messages

New parameter for netlink.get() method -- interruptible.
Please note, that setting this parameter will cause polling
overhead.

Bug-Url: http://bugs.python.org/issue1360