BProxySecureSocket: Fix obviously untested code.

* Actually set status before testing it
* sscanf (reads from passed buffer) not scanf (reads from stdin)
* &httpStatus not httpStatus.

Found by Coverity.

libbnetapi: Extend socket classes.

B{Abstract,Datagram,Secure}Socket:
- Add functionality to listen for and accept new connections, thus allowing
one to use the socket classes for server functionality as well.

BSecureSocket:
- Adjust to take into account differences between how SSL needs to be called
when accepting an incoming connection vs initiating an outbound one.
The handshake on the accepted connection stills fails for unknown reasons
at the moment though.

Note that these changes break the ABI, and thus any packages making use of
them directly will need a rebuild.

Implement CONNECT pass-through for HTTPS proxy

* When using a proxy, HTTPS connexion must still go directly to the
target website. The proxy can then act as a TCP stream relay and just
transmit the raw SSL stream between the client and website.
* For this, we ask the proxy sending an HTTP request with the CONNECT
method. If the proxy supports this, we can then send anything as the
payload and it will be forwarded.
* Untested, as the network here in Dusseldorf doesn't let me use a
proxy.

ticket : #10973