Close telnet connections which do not log in promptly

When an inbound telnet connection is made, a timer should be started and the connection closed if no successful login has occurred within some (probably small) amount of time.

Background:

We ended up with a whole bunch of connection objects in `$.servers.telnet.connected`. Looking at their `.buffer` property, I could see that something had connected to port 7777 and spammed some random binary data, but without a newline character to trigger a call to `.onReceiveLine`. This had apparently happened ca. 1400 times.

I did an eval to call .close on these connection objects; ~700 of them were apparently still attached to open connections, and calling .close caused them to be closed and then removed from the `.connected` list by their .onClose handler. The other ~700 had `.connected` set to true but were apparently not actually connected to anything so calling `.close` did not result in their `.onClose` being called. I set their `.open = false` manually, causing them to be cleared from the list the next time an actual connection dropped.