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 for session_reap() to make a sweep and check for changes
in requests that are now complete as a side-effect of checking for
completed requests.

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