Multisession blocking repair

Multisession blocking repair

The new socket blocking code for multisession failed to take into
account that socket activity outside of the main block could lead to a
deadlock situation.  For example:

* Check status of request A -> not complete
* Check status of request B -> whatever
* Request A may now be complete, since checking the status of any request
  affects all requests
* Return to blocking loop because we think there is pending data, but in
  fact all data has already been pulled from the socket.

The solution is to make a sweep and check for changes in requests
without touching the socket after all of the socket-fiddling is done.

Signed-off-by: Bill Erickson <berick@esilibrary.com>