Session deadlocks if both initiator and acceptor enter the resend state

[mgatny]

If both initiator and acceptor request resend at the same time (e.g. at logon):

• neither resend request will be satisfied
• no heartbeats will be exchanged
• no disconnect will occur
• no message flow, errors, or progress of any kind will occur

Update: this may be fixed by bhaan's latest changes. Need to re-test.

[cbusbey]

Refs #164 #165 #167