Follow up r1206: don't register clean_conn as child_cleanup.  In the case an application using serf execs a child process,  this causes the child close socket(s) still used/needed by the parent.
Follow up r1206: don't register clean_conn as child_cleanup. 
In the case an application using serf execs a child process, 
this causes the child close socket(s) still used/needed by
the parent.

This fixes subversion issue #3424.

* outgoing.c
  (serf_connection_create): don't register a child-exec cleanup
   handler for connections.
jandre/serf,jandre/serf,jandre/serf,jandre/serf