Log Message:
Updated py-foolscap to 0.12.3.

* Release 0.12.3 (01-Sep-2016)

** Improvements

The `tor.socks_port()` handler was replaced by `tor.socks_endpoint()`, which
takes an Endpoint object (just like `tor.control_endpoint()` does). This
enables applications to speak SOCKS to the Tor daemon over e.g. a Unix-domain
socket. The `tor.socks_port()` API was removed, so applications using it must
upgrade. #265

The `allocate_tcp_port()` utility function would occasionally return ports
that were in use by other applications, when those applications bound their
own port to the loopback interface (127.0.0.1). allocate_tcp_port should no
longer do this.