canilisten should catch more errors

[aaaaalbert]

The code in the canilisten library needs to be reviewed for potential missing error handling. I saw this recently:

Uncaught exception!

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Following is a full traceback, and a user traceback.
The user traceback excludes non-user modules. The most recent call is displayed last.

Full debugging traceback:
  "repyV2/repy.py", line 154, in execute_namespace_until_completion
  "/home/poly_seattlenatforwarder/seattle/seattle_repy/repyV2/virtual_namespace.py", line 117, in evaluate
  "/home/poly_seattlenatforwarder/seattle/seattle_repy/repyV2/safe.py", line 588, in safe_run
  "dylink.r2py", line 546, in <module>
  "dylink.r2py", line 407, in dylink_dispatch
  "dylink.r2py", line 520, in evaluate
  "/home/poly_seattlenatforwarder/seattle/seattle_repy/repyV2/virtual_namespace.py", line 117, in evaluate
  "/home/poly_seattlenatforwarder/seattle/seattle_repy/repyV2/safe.py", line 588, in safe_run
  "tcp_relay.r2py", line 672, in <module>
  "canilisten.r2py", line 381, in check_specific_port
  "canilisten.r2py", line 424, in check_port_with_specific_server
  "canilisten.r2py", line 529, in request_connection_and_get_apparent_address
  "session.r2py", line 31, in session_recvmessage
  "sockettimeout.r2py", line 117, in recv

User traceback:
  "dylink.r2py", line 546, in <module>
  "dylink.r2py", line 407, in dylink_dispatch
  "dylink.r2py", line 520, in evaluate
  "tcp_relay.r2py", line 672, in <module>
  "canilisten.r2py", line 381, in check_specific_port
  "canilisten.r2py", line 424, in check_port_with_specific_server
  "canilisten.r2py", line 529, in request_connection_and_get_apparent_address
  "session.r2py", line 31, in session_recvmessage
  "sockettimeout.r2py", line 117, in recv

Exception (with class '.SocketTimeoutError'): recv() timed out!!

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[aaaaalbert]

Fixed in fde56b8. Closing.