Telnet server accumulated dead connections

[cpcallen]

Because:

• There is no builtin to get a list of open connections, and
• There is no builtin to test to see if a given connection is still open, and
• There are certain circumstances under which the .onClose method of a connection object may not be successfully run to completion (such as when the connection is closed by virtue of the server being shut down)

there is a tendency for $.servers.telnet.connections to fill up with a lot of cruft, which in turn shows up on the $.console display.

Some effort was made previously to mitigate this, but it has evidently not been sufficient. See if it's possible to make this work well-enough in-database, or open a new bug to provide the necessary builtins.

[cpcallen]

I've created$.servers.telnet.validate, which, along with related changes to $.servers.telnet.connection and its prototype $.connection, should keep the list of connected connections reasonably accurate.

[cpcallen]

Seems like this is not fixed: there's a whole bunch of / connections listed on the console again.