Update code in doc/ directory to use new application

[hypatia]

Here's the result of a trivial grep:

howto/listings/manhole/manhole1.py:from twisted.internet.app import Application
howto/listings/manhole/manhole2.py:from twisted.internet.app import Application
howto/listings/manhole/manhole3.py:from twisted.internet.app import Application
howto/listings/pb/copy_receiver.py:from twisted.internet.app import Application
howto/listings/pb/cache_receiver.py:from twisted.internet.app import Application
howto/listings/pb/copy2_receiver.py:from twisted.internet.app import Application
howto/listings/pb/go_server.py:import twisted.internet.app
howto/listings/pb/go_server.py:    app =
twisted.internet.app.Application("go_server")
howto/listings/pb/pb4server.py:import twisted.internet.app
howto/listings/pb/pb4server.py:app = twisted.internet.app.Application("pb4server")
howto/listings/pb/pb7server.py:import twisted.internet.app
howto/listings/pb/pb7server.py:app = twisted.internet.app.Application("pb7server")
howto/listings/pb/pb7server.py:multi =
twisted.internet.app.MultiService("shared", app)

Yuck.

[hypatia]

OK, the manhole examples were removed, and copy_receiver.py, cache_receiver.py,
copy2_receiver.py and pb4server.py updated.

go_server.py and pb7server.py need to be updated to newcred, which probably
means I'll port them to the new PB API at the same time that I port them to new
application.

[hypatia]

go_server and pb7server weren't used by current HOWTOs anyway: removed them.

Marked bug done.

[Craig Rodrigues <rodrigc@…>]

In 9481baa4:

Error: Processor CommitTicketReference failed

 does not appear to be a Git repository. See the log for more information.