Fix error with modern Python 2.X versions:

TypeError: exceptions must be old-style classes or derived from
BaseException, not str

Thus, we are not allowed to raise a string. Raise Exception instead.
Renamed CustomProxyServer to WebSocketProxy; this was the earlier name.

Also, call the server instance "server", not "httpd", even when using
LibProxyServer.
Corrected last commit.
Merge branch 'master' of github.com:astrand/websockify
Rename self.client to self.request, ie adapt to:

>commit b9e1295f7afa34a4c69618609e053af154e477d7
>    Prepare for solving https://github.com/kanaka/websockify/issues/71:
>
>    Rename self.client to self.request, since this is what standard
>    SocketServer request handlers are using.
Make echo.py and load.py work again, after the refactoring of
websocket.py:

* With echo.py, which doesn't need any server configuration, we can
  just switch over our application class to inherit from
  WebSocketRequestHandler instead of WebSocketServer. Also, need to
  use the new method name new_websocket_client.

* With load.py, since we have the "delay" configuration, we need both
  a server class and a request handler.

Note that for both tests, I've removed the raising of
self.EClose(closed). This is incorrect. First of all, it's described
as "An exception before the WebSocket connection was established", so
not suitable for our case. Second, it will cause send_close to be
called twice. Finally, self.EClose is now in the WebSocketServer
class, and not a member of the request handler.