* When a session kills itself (for example, due to a broken socket),

* When a session kills itself (for example, due to a broken socket),
  force the dead_session_purge() to run immediately.  This avoids
  thousands of error messages for up to the next five seconds while it
  waits for the next purge.
* For the main select() loop, we can now recover from EBADF by jumping
  back to the code that scans for valid descriptors.  (Yeah, I used a
  goto.  It's more readable that way, so STFU if you have a problem with
  it.)