[NTTCP-2] Network.Transport.TCP may reject incoming connection request

[Imported from JIRA. Reported by Edsko de Vries @edsko) as NTTCP-2 on 2012-09-24 11:35:00]
Suppose A and B are connected, but the connection breaks. When A realizes this immediately and sends a new (heavyweight) connection request to B, then it /might/ happen that B has not yet realized that the current connection has broken and will therefore reject the incoming request from A as invalid.

This is low priority because

• the window of opportunity for the problem to occur is small, especially because in the case of a true network failure it will take some time before a new connection can be established
• even if the problem does arise, A can simply try to connect again (A might have to that anyway, to find out if the network problem has been resolved).

Start by locating the Network.Transport.TCP implementation and tracing how incoming heavyweight connection requests are validated when an existing connection has broken. Reproduce the timing window if possible, then add coverage showing that a valid replacement request is accepted or that the connection state is handled consistently.