Currently we have the following methods:

* socket.settimeout(t) -- can set the socket in blocking mode, when t==0.
* socket.setblocking(flag) -- sets in blocking or non-blocking mode.
* socket.gettimeout() -- returns 0 when socket is in non-blocking mode.

socket.gettimeout() is the only easy way of checking if the socket is non-blocking or blocking, but it's not intuitive to use it.  It's especially strange that we have a setblocking() method without a corresponding getblocking().

I propose to add a 'socket.getblocking() -> bool' method.