Forgot to mention in my previous post..

Having subclasses for certain proxy profiles as described in msg83 could possibly be convenient,
and the system described in my previous post would be forward-compatible with such a system.  As
a hypothetical example, a call to define_proxy_profile might look like this:

   define_proxy_profile("myproxy", new http_proxy(1080));

Note that it is not necessary to implement such subclasses for the functioning of the system, and
they only provide a kind of shorthand notation.  But if we leave the possibility open, we may decide
later on that they are a feature worth having.