Fix a pipelining bug that occurs if we push in a request while we are processing another request that is not completed.
Fix a pipelining bug that occurs if we push in a request while we are
processing another request that is not completed.

* context.c
  (read_from_connection): If we switched to a new request, update the
  pollset unconditionally.  Otherwise, the pollset might not know that
  we have data to write this time around.

jandre/serf,jandre/serf,jandre/serf,jandre/serf