Fix 100% CPU usage with many pipelined requests.
Fix 100% CPU usage with many pipelined requests.

* outgoing.c
  (write_to_connection): Mark pollset as dirty if we reached probable 
   keep-alive limit.
  (read_from_connection): Mark pollset as dirty when completed_responses 
   is changed.

blueszhangsh/serf,idomon/serf,wzugang/serf,justinweb/serf,liuzongquan/serf,liuzongquan/serf,TommyU/serf,TommyU/serf,sworda/serf,idomon/serf,Manouchehri/serf,wzugang/serf,wzugang/serf,liuzongquan/serf,TommyU/serf,idomon/serf,Manouchehri/serf,muthusuba/serf,justinweb/serf,Manouchehri/serf,blueszhangsh/serf,muthusuba/serf,muthusuba/serf,krime/serf,justinweb/serf,krime/serf,sworda/serf,blueszhangsh/serf,TommyU/serf,sworda/serf,idomon/serf,muthusuba/serf,sworda/serf,krime/serf,liuzongquan/serf,wzugang/serf,krime/serf,blueszhangsh/serf,justinweb/serf,Manouchehri/serf