Enable serf_get to take extra request headers.
Enable serf_get to take extra request headers.

Patch by: David Disseldorp

* test/serf_get.c
  (handler_baton_t): Add req_hdrs members.
  (append_request_headers): New function.
  (setup_request): Add extra headers to the request.
  (print_usage, main): Add -r option.

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