GProxyConnection is a class that was added for proxy support;
g_socket_client_connect() returns a GSocketConnection, but in some
cases (eg, encrypted SOCKS), GProxy might return a GIOStream that is
not a GSocketConnection. In that case, GSocketClient would wrap the
stream up in a GProxyConnection, which is a subclass of
GSocketConnection but uses the input/output streams of the wrapped
connection.

GTlsConnection is not a GSocketConnection, so it has the same problem,
so it will need the same treatment. Rename the class to
GTcpWrapperStream, and make it public, so people can extract the base
stream from it when necessary.

(This is not ideal and GSocketClient will need to be revisited as an
API at some point...)

https://bugzilla.gnome.org/show_bug.cgi?id=588189